Andingeneraleachoftheseanimalsnaturallytendstowardssterility。Theasshasallthedisadvantagesalreadymentioned，andifitshouldnotbegintogenerateafterthefirstsheddingofteeth，itnolongergeneratesatall；sonearistheconstitutionoftheasstobeingsterile。Thehorseismuchthesame；ittendsnaturallytowardssterility，andtomakeitentirelysoitisonlynecessarythatitsgenerativesecretionshouldbecomecolder；nowthisiswhathappenstoitwhenmixedwiththecorrespondingsecretionoftheass。Theassinlikemannercomesveryneargeneratingasterileanimalwhenmatedwithitsownspecies。Thuswhenthedifficultyofacrosscontrarytonatureisadded，（whentooevenintheothercasewhenunitedwiththeirownspeciestheywithdifficultyproduceasingleyoungone），theresultofthecross，beingstillmoresterileandcontrarytonature，willneednothingfurthertomakeitsterile，butwillbesoofnecessity。
　　Wefindalsothatthebodiesoffemalemulesgrowlargebecausethematterwhichissecretedinotheranimalstoformthecatameniaisdivertedtogrowth。Butsincetheperiodofgestationinsuchanimalsisayear，themulemustnotonlyconceive，ifsheistobefertile，butmustalsonourishtheembryotillbirth，andthisisimpossibleiftherearenocatamenia。Buttherearenoneinthemule；theuselesspartofthenutrimentisdischargedwiththeexcretionfromthebladder—thisiswhymalemulesdonotsmelltothepudendaofthefemales，asdotheothersolid—hoofedungulates，butonlytotheevacuationitself—andtherestofthenutrimentisuseduptoincreasethesizeofthebody。Henceitissometimespossibleforthefemaletoconceive，ashasbeenknowntohappenbeforenow，butitisimpossibleforhertocompletetheprocessofnourishingtheembryoandbringingittobirth。
　　Themale，again，maysometimesgenerate，bothbecausethemalesexisnaturallyhotterthanthefemaleandbecauseitdoesnotcontributeanymaterialsubstancetothemixture。Theresultinsuchcasesisa’ginnus’，thatistosay，adwarfmule；for’ginni’areproducedalsofromthecrossingofhorseandasswhentheembryoisdiseasedintheuterus。Theginnusisinfactliketheso—called’metachoera’inswine，fora’metachoerum’alsoisapiginjuredintheuterus；thismayhappentoanypig。Theoriginofhumandwarfsissimilar，forthesealsohavetheirpartsandtheirwholedevelopmentinjuredduringgestation，andresembleginniandmetachoera。
　　BookIII
　　1
　　WEhavenowspokenaboutthesterilityofmules，andaboutthoseanimalswhichareviviparousbothexternallyandwithinthemselves。
　　Thegenerationoftheoviparoussanguineaistoacertainextentsimilartothatoftheanimalsthatwalk，andallmaybeembracedinthesamegeneralstatement；butinotherrespectstherearedifferencesinthembothascomparedwitheachotherandwiththosethatwalk。Allalikearegeneratedfromsexualunion，themaleemittingsemenintothefemale。Butamongtheovipara（1）birdsproduceaperfecthard—shelledegg，unlessitbeinjuredbydisease，andtheeggsofbirdsarealltwo—coloured。（2）Thecartilaginousfishes，ashasbeenoftensaidalready，areoviparousinternallybutproducetheyoungalive，theeggchangingpreviouslyfromonepartoftheuterustoanother；andtheireggissoft—shelledandofonecolour。Oneofthisclassalonedoesnotproducetheyoungfromtheeggwithinitself，theso—called’frog’；thereasonofwhichmustbestatedlater。（3）Allotheroviparousfishesproduceaneggofonecolour，butthisisimperfect，foritsgrowthiscompletedoutsidethemother’sbodybythesamecauseasarethoseeggswhichareperfectedwithin。
　　Concerningtheuterusoftheseclassesofanimals，whatdifferencesthereareamongthemandforwhatreasons，hasbeenstatedpreviously。Forinsomeoftheviviparouscreaturesitishighupnearthehypozoma，inotherslowdownbythepudenda；theformerinthecartilaginousfishes，thelatterinanimalsbothinternallyandexternallyviviparous，suchasmanandhorseandtherest；intheoviparaitissometimeslow，asintheoviparousfish，andsometimeshigh，asinbirds。
　　Someembryosareformedinbirdsspontaneously，whicharecalledwind—eggsand’zephyria’bysome；theseoccurinbirdswhicharenotgiventoflightnorrapinebutwhichproducemanyyoung，forthesebirdshavemuchresidualmatter，whereasinthebirdsofpreyallsuchsecretionisdivertedtothewingsandwing—feathers，whilethebodyissmallanddryandhot。（Thesecretioncorrespondinginhen—birdstocatamenia，andthesemenofthecock，areresidues。）Sincethenboththewingsandthesemenaremadefromresidualmatter，naturecannotaffordtospendmuchuponboth。Andforthissamereasonthebirdsofpreyareneithergiventotreadingmuchnortolayingmanyeggs，asaretheheavybirdsandthoseflyingbirdswhosebodiesarebulky，asthepigeonandsoforth。Forsuchresidualmatterissecretedlargelyintheheavybirdsnotgiventoflying，suchasfowls，partridges，andsoon，whereforetheirmalestreadoftenandtheirfemalesproducemuchmaterial。Ofsuchbirdssomelaymanyeggsatatimeandsomelayoften；forinstance，thefowl，thepartridge，andtheLibyanostrichlaymanyeggs，whilethepigeonfamilydonotlaymanybutlayoften。Forthesearebetweenthebirdsofpreyandtheheavyones；theyareflyersliketheformer，buthavebulkybodieslikethelatter；hence，becausetheyareflyersandtheresidueisdivertedthat。way，theylayfeweggs，buttheylayoftenbecauseoftheirhavingbulkybodiesandtheirstomachsbeinghotandveryactiveinconcoction，andbecausemoreovertheycaneasilyprocuretheirfood，whereasthebirdsofpreydosowithdifficulty。
　　Smallbirdsalsotreadoftenandareveryfertile，asaresometimessmallplants，forwhatcausesbodilygrowthinothersturninthemtoaseminalresiduum。HencetheAdrianicfowlslaymosteggs，forbecauseofthesmallnessoftheirbodiesthenutrimentisusedupinproducingyoung。Andotherbirdsaremorefertilethangame—fowl，fortheirbodiesaremorefluidandbulkier，whereasthoseofgame—fowlareleaneranddrier，sinceapassionatespiritisfoundratherinsuchbodiesasthelatter。Moreoverthethinnessandweaknessofthelegscontributetomakingtheformerclassofbirdsnaturallyinclinedtotreadandtobefertile，aswefindalsointhehumanspecies；forthenourishmentwhichotherwisegoestothelegsisturnedinsuchintoaseminalsecretion，whatNaturetakesfromtheoneplacebeingaddedattheother。Birdsofprey，onthecontrary，haveastrongwalkandtheirlegsarethickowingtotheirhabits，sothatforallthesereasonstheyneithertreadnorlaymuch。
　　Thekestrelisthemostfertile；forthisisnearlytheonlybirdofpreywhichdrinks，anditsmoisture，bothinnateandacquired，alongwithitsheatisfavourabletogenerativeproducts。Eventhisbirddoesnotlayverymanyeggs，butfourattheoutside。
　　Thecuckoo，thoughnotabirdofprey，laysfeweggs，becauseitisofacoldnature，asisshownbythecowardiceofthebird，whereasagenerativeanimalshouldbehotandmoist。Thatitiscowardlyisplain，foritispursuedbyallthebirdsandlayseggsinthenestsofothers。
　　Thepigeonfamilyareinthehabitoflayingtwoforthemostpart，fortheyneitherlayone（nobirddoesexceptthecuckoo，andeventhatsometimeslaystwo）noryetmany，buttheyfrequentlyproducetwo，orthreeatthemostgenerallytwo，forthisnumberliesbetweenoneandmany。
　　Itisplainfromthefactsthatwiththebirdsthatlaymanyeggsthenutrimentisdivertedtothesemen。Formosttrees，iftheybeartoomuchfruit，witherawayafterthecropwhennutrimentisnotreservedforthemselves，andthisseemstobewhathappenstoannuals，asleguminousplants，corn，andthelike。Fortheyconsumealltheirnutrimenttomakeseed，theirkindbeingprolific。Andsomefowlsafterlayingtoomuch，soaseventolaytwoeggsinaday，havediedafterthis。Forboththebirdstheplantsbecomeexhausted，andthisconditionisanexcessofsecretionofresidualmatter。Asimilarconditionisthecauseofthelatersterilityofthelioness，foratthefirstbirthsheproducesfiveorsix，theninthenextyearfour，andagainthreecubs，thenthenextnumberdowntoone，thennoneatall，showingthattheresidueisbeingusedupandthegenerativesecretionisfailingalongwiththeadvanceofyears。
　　Wehavenowstatedinwhichbirdswind—eggsarefound，andalsowhatsortofbirdslaymanyeggsorfew，andforwhatreasons。Andwind—eggs，assaidbefore，comeintobeingbecausewhileitisthematerialforgenerationthatexistsinthefemaleofallanimals，birdshavenodischargeofcatamenialikeviviparoussanguinea（fortheyoccurinalltheselatter，moreinsome，lessinothers，andinsomeonlyenoughinquantityjusttomarktheclass）。Thesameappliestofishastobirds，andsointhemasinbirdsisfoundanembryonicformationwithoutimpregnation，butitislessobviousbecausetheirnatureiscolder。Thesecretioncorrespondingtothecatameniaofviviparaisformedinbirdsattheappropriateseasonforthedischargeofsuperfluousmatter，and，becausetheregionnearthehypozomaishot，itisperfectedsofarassizeisconcerned，butinbirdsandfishesalikeitisimperfectforgenerationwithouttheseminalfluidofthemale；thecauseofthishasbeenpreviouslygiven。Wind—eggsarenotformedintheflyingbirds，forthesamereasonaspreventstheirlayingmanyeggs；fortheresidualmatterinbirdsofpreyissmall，andtheyneedthemaletogiveanimpulseforthedischargeofit。Thewind—eggsareproducedingreaternumbersthantheimpregnatedbutsmallerinsizeforoneandthesamereason；theyaresmallerinsizebecausetheyareimperfect，andbecausetheyaresmallerinsizetheyaremoreinnumber。Theyarelesspleasantforfoodbecausetheyarelessconcocted，forinallfoodstheconcoctedismoreagreeable。Ithasbeensufficientlyobserved，then，thatneitherbirds’norfishes’eggsareperfectedforgenerationwithoutthemales。Asforembryosbeingformedinfishalso（thoughinalessdegree）withoutthemales，thefacthasbeenobservedespeciallyinriverfish，forsomeareseentohaveeggsfromthefirst，ashasbeenwrittenintheEnquiriesconcerningthem。Andgenerallyspeakinginthecaseofbirdseventheimpregnatedeggsarenotwontforthemostparttoattaintheirfullgrowthunlessthehenbetroddencontinually。Thereasonofthisisthatjustaswithwomenintercoursewithmendrawsdownthesecretionofthecatamenia（fortheuterusbeingheatedattractsthemoistureandthepassagesareopened），sothishappensalsowithbirds；theresidualmattercorrespondingtothecatameniaadvancesalittleatatime，andisnotdischargedexternally，becauseitsamountissmallandtheuterusishighupbythehypozoma，buttricklestogetherintotheuterusitself。Forastheembryooftheviviparagrowsbymeansoftheumbilicalcord，sotheegggrowsthroughthismatterflowingtoitthroughtheuterus。Forwhenoncethehenshavebeentrodden，theyallcontinuetohaveeggsalmostwithoutintermission，thoughverysmallones。Hencesomearewonttospeakofwind—eggsasnotcomingintobeingindependentlybutasmererelicsfromapreviousimpregnation。Butthisisafalseview，forsufficientobservationshavebeenmadeoftheirarisingwithoutimpregnationinchickensandgoslings。Alsothefemalepartridgeswhicharetakenouttoactasdecoys，whethertheyhaveeverbeenimpregnatedornot，immediatelyonsmellingthemaleandhearinghiscall，becomefilledwitheggsinthelattercaseandlaythemintheformer。Thereasonwhythishappensisthesameasinmenandquadrupeds，foriftheirbodieschancetobeinruttheyemitsemenatthemeresightofthefemaleorataslighttouch。Andsuchbirdsareofalasciviousandfertilenature，sothattheimpulsetheyneedisbutsmallwhentheyareinthisexcitedcondition，andthesecretingactivitytakesplacequicklyinthem，wind—eggsformingintheunimpregnatedandtheeggsinthosewhichhavebeenimpregnatedgrowingandreachingperfectionswiftly。
　　Amongcreaturesthatlayeggsexternallybirdsproducetheireggperfect，fishimperfect，buttheeggsofthelattercompletetheirgrowthoutsideashasbeensaidbefore。Thereasonisthatthefishkindisveryfertile；nowitisimpossibleformanyeggstoreachcompletionwithinthemotherandthereforetheylaythemoutside。Theyarequicklydischarged，fortheuterusofexternallyoviparousfishesisnearthegenerativepassage。Whiletheeggsofbirdsaretwo—coloured，thoseofallfishareone—coloured。Thecauseofthedoublecolourmaybeseenfromconsideringthepowerofeachofthetwoparts，thewhiteandtheyolk。Forthematteroftheeggissecretedfromtheblood[Nobloodlessanimallayseggs，]andthatthebloodisthematerialofthebodyhasbeenoftensaidalready。Theonepart，then，oftheeggisnearertheformoftheanimalcomingintobeing，thatisthehotpart；themoreearthypartgivesthesubstanceofthebodyandisfurtherremoved。Henceinalltwo—colouredeggstheanimalreceivesthefirstprincipleofgenerationfromthewhite（forthevitalprincipleisinthatwhichishot），butthenutrimentfromtheyolk。Nowinanimalsofahotternaturethepartfromwhichthefirstprinciplearisesisseparatedofffromthepartfromwhichcomesthenutriment，theonebeingwhiteandtheotheryellow，andthewhiteandpureisalwaysmorethantheyellowandearthy；butinthemoisterandlesshottheyolkismoreinquantityandmorefluid。Thisiswhatwefindinlakebirds，fortheyareofamoisternatureandarecolderthanthelandbirds，sothattheso—called’lecithus’oryolkintheeggsofsuchbirdsislargeandlessyellowbecausethewhiteislessseparatedofffromit。Butwhenwecometotheoviparawhicharebothofacoldnatureandalsomoister（suchisthefishkind）wefindthewhitenotseparatedatallbecauseofthesmallsizeoftheeggsandthequantityofthecoldandearthymatter；thereforeallfisheggsareofonecolour，andwhitecomparedwithyellow，yellowcomparedwithwhite。Eventhewind—eggsofbirdshavethisdistinctionofcolour，fortheycontainthatoutofwhichwillcomeeachofthetwoparts，alikethatwhencearisestheprincipleoflifeandthatwhencecomesthenutriment；onlyboththeseareimperfectandneedtheinfluenceofthemaleinaddition；forwind—eggsbecomefertileifimpregnatedbythemalewithinacertainperiod。Thedifferenceincolour，however，isnotduetoanydifferenceofsex，asifthewhitecamefromthemale，theyolkfromthefemale；bothonthecontrarycomefromthefemale，buttheoneiscold，theotherhot。
　　Inallcasesthenwherethehotpartisconsiderableitisseparatedoff，butwhereitislittleitcannotbeso；hencetheeggsofsuchanimals，ashasbeensaid，areofonecolour。Thesemenofthemaleonlyputsthemintoform；andthereforeatfirsttheegginbirdsappearswhiteandsmall，butasitadvancesitisallyellowasmoreofthesanguineousmaterialiscontinuallymixedwithit；finallyasthehotpartisseparatedthewhitetakesupapositionallrounditandequallydistributedonallsides，aswhenaliquidboils；forthewhiteisnaturallyliquidandcontainsinitselfthevitalheat；
　　thereforeitisseparatedoffallround，buttheyellowandearthypartisinside。Andifweenclosemanyeggstogetherinabladderorsomethingofthekindandboilthemoverafiresoasnottomakethemovementoftheheatquickerthantheseparationofthewhiteandyolkintheeggs，thenthesameprocesstakesplaceinthewholemassoftheeggsasinasingleegg，alltheyellowpartcomingintothemiddleandthewhitesurroundingit。
　　Wehavethusstatedwhysomeeggsareofonecolourandothersoftwo。
　　2
　　Theprincipleofthemaleisseparatedoffineggsatthepointwheretheeggisattachedtotheuterus，andthereasonwhytheshapeoftwo—colouredeggsisunsymmetrical，andnotperfectlyroundbutsharperatoneend，isthatthepartofthewhiteinwhichiscontainedthisprinciplemustdifferfromtherest。Thereforetheeggisharderatthispointthanbelow，foritisnecessarytoshelterandprotectthisprinciple。Andthisiswhythesharpendoftheeggcomesoutofthehenlaterthanthebluntend；forthepartattachedtotheuteruscomesoutlater，andtheeggisattachedatthepointwhereisthesaidprinciple，andtheprincipleisinthesharpend。
　　Thesameisthecasealsointheseedsofplants；theprincipleoftheseedisattachedsometimestothetwig，sometimestothehusk，sometimestothepericarp。Thisisplainintheleguminousplants，forwherethetwocotyledonsofbeansandofsimilarseedsareunited，thereistheseedattachedtotheparentplant，andthereistheprincipleoftheseed。
　　Adifficultymayberaisedaboutthegrowthoftheegg；howisitderivedfromtheuterus？Forifanimalsderivetheirnutrimentthroughtheumbilicalcord，throughwhatdoeggsderiveit？Theydonot，likeascolex，acquiretheirgrowthbytheirownmeans。Ifthereisanythingbywhichtheyareattachedtotheuterus，whatbecomesofthiswhentheeggisperfected？Itdoesnotcomeoutwiththeeggasthecorddoeswithanimals；forwhenitseggisperfectedtheshellformsallroundit。Thisproblemisrightlyraised，butitisnotobservedthattheshellisatfirstonlyasoftmembrane，andthatitisonlyaftertheeggisperfectedthatitbecomeshardandbrittle；thisissonicelyadjustedthatitisstillsoftwhenitcomesout（forotherwiseitwouldcausepaininlaying），butnosoonerhasitcomeoutthanitisfixedhardbycooling，themoisturequicklyevaporatingbecausethereisbutlittleofit，andtheearthypartremaining。Nowatfirstacertainpartofthismembraneatthesharpendofeggsresemblesanumbilicalcord，andprojectslikeapipefromthemwhiletheyarestillsmall。Itisplainlyvisibleinsmallabortedeggs，forifthebirdbedrenchedwithwaterorsuddenlychilledinanyotherwayandcastouttheeggtoosoon，itappearsstillsanguineousandwithasmalltaillikeanumbilicalcordrunningthroughit。Astheeggbecomeslargerthisismoretwistedroundandbecomessmaller，andwhentheeggisperfectedthisendisthesharpend。Underthisistheinnermembranewhichseparatesthewhiteandtheyolkfromthis。Whentheeggisperfected，thewholeofitissetfree，andnaturallytheumbilicalcorddoesnotappear，foritisnowtheextremeendoftheeggitself。
　　Theeggisdischargedintheoppositewayfromtheyoungofvivipara；thelatterarebornhead—first，thepartwhereisthefirstprincipleleading，buttheeggisdischargedasitwerefeetfirst；thereasonofthisbeingwhathasbeenstated，thattheeggisattachedtotheuterusatthepointwhereisthefirstprinciple。
　　Theyoungbirdisproducedoutoftheeggbythemother’sincubatingandaidingtheconcoction，thecreaturedevelopingoutofpartoftheegg，andreceivinggrowthandcompletionfromtheremainingpart。ForNaturenotonlyplacesthematerialofthecreatureintheeggbutalsothenourishmentsufficientforitsgrowth；forsincethemotherbirdcannotperfectheryoungwithinherselfsheproducesthenourishmentintheeggalongwithit。Whereasthenourishment，whatiscalledmilk，isproducedfortheyoungofviviparainanotherpart，inthebreasts，Naturedoesthisforbirdsintheegg。
　　Theopposite，however，isthecasetowhatpeoplethinkandwhatisassertedbyAlcmaeonofCrotona。Foritisnotthewhitethatisthemilk，buttheyolk，foritisthisthatisthenourishmentofthechick，whereastheythinkitisthewhitebecauseofthesimilarityofcolour。
　　Thechickthen，ashasbeensaid，comesintobeingbytheincubationofthemother；yetifthetemperatureoftheseasonisfavourable，oriftheplaceinwhichtheeggshappentolieiswarm，theeggsaresufficientlyconcoctedwithoutincubation，boththoseofbirdsandthoseofoviparousquadrupeds。Forthesealllaytheireggsupontheground，wheretheyareconcoctedbytheheatintheearth。Suchoviparousquadrupedsasdovisittheireggsandincubatedosoratherforthesakeofprotectingthemthanofincubation。
　　Theeggsofthesequadrupedsareformedinthesamewayasthoseofbirds，fortheyarehard—shelledandtwo—coloured，andtheyareformednearthehypozomaasarethoseofbirds，andinallotherrespectsresemblethembothinternallyandexternally，sothattheinquiryintotheircausesisthesameforall。Butwhereastheeggsofquadrupedsarehatchedoutbythemereheatoftheweatherowingtotheirstrength，thoseofbirdsaremoreexposedtodestructionandneedthemother—bird。Natureseemstowishtoimplantinanimalsaspecialsenseofcarefortheiryoung：intheinferioranimalsthislastsonlytothemomentofgivingbirthtotheincompletelydevelopedanimal；inothersitcontinuestilltheyareperfect；inallthataremoreintelligent，duringthebringingupoftheyoungalso。Inthosewhichhavethegreatestportioninintelligencewefindfamiliarityandloveshownalsotowardstheyoungwhenperfected，aswithmenandsomequadrupeds；withbirdswefindittilltheyhaveproducedandbroughtuptheiryoung，andthereforeifthehensdonotincubateafterlayingtheygetintoworsecondition，asifdeprivedofsomethingnaturaltothem。
　　Theyoungisperfectedwithintheeggmorequicklyinsunshinyweather，theseasonaidinginthework，forconcoctionisakindofheat。Fortheearthaidsintheconcoctionbyitsheat，andthebroodinghendoesthesame，forsheappliestheheatthatiswithinher。Anditisinthehotseason，asweshouldexpect，thattheeggsaremoreapttobespoiltandtheso—called’uria’orrotteneggsareproduced；forjustaswinesturnsourintheheatsfromthesedimentrising（forthisisthecauseoftheirbeingspoilt），soisitwiththeyolkineggs，forthesedimentandyolkaretheearthypartineachcase，whereforethewinebecomesturbidwhenthesedimentmixeswithit，andthelikeappliestotheeggsthatarespoilingbecauseoftheyolk。Itisnaturalthenthatsuchshouldbethecasewiththebirdsthatlaymanyeggs，foritisnoteasytogivethefittingamountofheattoall，but（whilesomehavetoolittle）
　　othershavetoomuchandthismakesthemturbid，asitwerebyputrefaction。Butthishappensnonethelesswiththebirdsofpreythoughtheylayfeweggs，foroftenoneofthetwobecomesrotten，andthethirdpracticallyalways，forbeingofahotnaturetheymakethemoistureintheeggstooverboilsotosay。Forthenatureofthewhiteisopposedtothatoftheyolk；theyolkcongealsinfrostsbutliquefiesonheating，andthereforeitliquefiesonconcoctionintheearthorbyreasonofincubation，andbecomingliquidservesasnutrimentforthedevelopingchick。Ifexposedtoheatandroasteditdoesnotbecomehard，becausethoughearthyinnatureitisonlysointhesamewayaswaxis；accordinglyonheatingtoomuchtheeggsbecomewateryandrotten，[iftheybenotfromaliquidresidue]。Thewhiteonthecontraryisnotcongealedbyfrostbutratherliquefies（thereasonofwhichhasbeenstatedbefore），butonexposuretoheatbecomessolid。Thereforebeingconcoctedinthedevelopmentofthechickitisthickened。Foritisfromthisthattheyoungisformed（whereastheyolkturnstonutriment）anditisfromthisthatthepartsderivetheirgrowthastheyareformedoneafteranother。Thisiswhythewhiteandtheyolkareseparatedbymembranes，asbeingdifferentinnature。Theprecisedetailsoftherelationofthepartstooneanotherbothatthebeginningofgenerationandastheanimalsareforming，andalsothedetailsofthemembranesandumbilicalcords，mustbelearntfromwhathasbeenwrittenintheEnquiries；forthepresentinvestigationitissufficienttounderstandthismuchclearly，that，whenthehearthasbeenfirstformedandthegreatblood—vesselhasbeenmarkedofffromit，twoumbilicalcordsrunfromthevessel，theonetothemembranewhichenclosestheyolk，theothertothemembraneresemblingachorionwhichsurroundsthewholeembryo；
　　thislatterrunsroundontheinsideofthemembraneoftheshell。
　　Throughtheoneofthesetheembryoreceivesthenutrimentfromtheyolk，andtheyolkbecomeslarger，foritbecomesmoreliquidbyheating。Thisisbecausethenourishment，beingofamaterialcharacterinitsfirstform，mustbecomeliquidbeforeitcanbeabsorbed，justasitiswithplants，andatfirstthisembryo，whetherinaneggorinthemother’suterus，livesthelifeofaplant，foritreceivesitsfirstgrowthandnourishmentbybeingattachedtosomethingelse。
　　Thesecondumbilicalcordrunstothesurroundingchorion。Forwemustunderstandthat，inthecaseofanimalsdevelopedineggs，thechickhasthesamerelationtotheyolkastheembryooftheviviparahastothemothersolongasitiswithinthemother（forsincethenourishmentoftheembryooftheoviparaisnotcompletedwithinthemother，theembryotakespartofitawayfromher）。Soalsotherelationofthechicktotheoutermostmembrane，thesanguineousone，islikethatofthemammalianembryototheuterus。
　　Atthesametimetheegg—shellsurroundsboththeyolkandthemembraneanalogoustotheuterus，justasifitshouldbeputroundboththeembryoitselfandthewholeofthemother，inthevivipara。
　　Thisissobecausetheembryomustbeintheuterusandattachedtothemother。Nowintheviviparatheuterusiswithinthemother，butintheoviparaitistheotherwayabout，asifoneshouldsaythatthemotherwasintheuterus，forthatwhichcomesfromthemother，thenutriment，istheyolk。Thereasonisthattheprocessofnourishmentisnotcompletedwithinthemother。
　　Asthecreaturegrowstheumbilicusrunningthechorioncollapsesfirst，becauseitisherethattheyoungistocomeout；whatisleftoftheyolk，andtheumbilicalcordrunningtotheyolk，collapselater。Fortheyoungmusthavenourishmentassoonasitishatched；
　　itisnotnursedbythemotherandcannotimmediatelyprocureitsnourishmentforitself；thereforetheyolkenterswithinitalongwithitsumbilicusandthefleshgrowsroundit。
　　Thisthenisthemannerinwhichanimalsproducedfromperfecteggsarehatchedinallthose，whetherbirdsorquadrupeds，whichlaytheeggwithahardshell。Thesedetailsareplainerinthelargercreatures；inthesmallertheyareobscurebecauseofthesmallnessofthemassesconcerned。
　　3
　　Theclassoffishesisalsooviparous。Thoseamongthemwhichhavetheuteruslowdownlayanimperfecteggforthereasonpreviouslygiven，’buttheso—called’selache’orcartilaginousfishesproduceaperfecteggwithinthemselvesbutareexternallyviviparousexceptonewhichtheycallthe’frog’；thisalonelaysaperfecteggexternally。Thereasonisthenatureofitsbody，foritsheadismanytimesaslargeastherestofthebodyandisspinyandveryrough。
　　Thisisalsowhyitdoesnotreceiveitsyoungagainwithinitselfnorproducethemalivetobeginwith，forasthesizeandroughnessoftheheadpreventstheirenteringsoitwouldpreventtheirexit。Andwhiletheeggofthecartilaginousfishesissoft—shelled（fortheycannothardenanddryitscircumference，beingcolderthanbirds），theeggofthefrog—fishaloneissolidandfirmtoprotectitoutside，butthoseoftherestareofamoistandsoftnature，fortheyareshelteredwithinandbythebodyofthemother。
　　Theyoungareproducedfromtheegginthesamewaybothwiththoseexternallyperfected（thefrog—fishes）andthoseinternally，andtheprocessintheseeggsispartlysimilarto，partlydifferentfromthatinbirds’eggs。Inthefirstplacetheyhavenotthesecondumbilicuswhichrunstothechorionunderthesurroundingshell。Thereasonofthisisthattheyhavenotthesurroundingshell，foritisnousetothemsincethemothersheltersthem，andtheshellisaprotectiontotheeggsagainstexternalinjurybetweenlayingandhatchingout。Secondly，theprocessinthesealsobeginsonthesurfaceoftheeggbutnotwhereitisattachedtotheuterus，asinbirds，forthechickisdevelopedfromthesharpendandthatiswheretheeggwasattached。Thereasonisthattheeggofbirdsisseparatedfromtheuterusbeforeitisperfected，butinmostthoughnotallcartilaginousfishestheeggisstillattachedtotheuteruswhenperfect。Whiletheyoungdevelopsuponthesurfacetheeggisconsumedbyitjustasinbirdsandtheotheranimalsdetachedfromtheuterus，andatlasttheumbilicusofthenowperfectfishisleftattachedtotheuterus。Thelikeisthecasewithallthosewhoseeggsaredetachedfromtheuterus，forinsomeofthemtheeggissodetachedwhenitisperfect。
　　Thequestionmaybeaskedwhythedevelopmentofbirdsandcartilaginousfishesdiffersinthisrespect。Thereasonisthatinbirdsthewhiteandyolkareseparate，butfisheggsareone—coloured，thecorrespondingmatterbeingcompletelymixed，sothatthereisnothingtostopthefirstprinciplebeingattheoppositeend，fortheeggisofthesamenaturebothatthepointofattachmentandattheoppositeend，anditiseasytodrawthenourishmentfromtheuterusbypassagesrunningfromthisprinciple。Thisisplainintheeggswhicharenotdetached，forinsomeofthecartilaginousfishtheeggisnotdetachedfromtheuterus，butisstillconnectedwithitasitcomesdownwardswithaviewtotheproductionoftheyoungalive；
　　inthesetheyoungfishwhenperfectedisstillconnectedbytheumbilicustotheuteruswhentheegghasbeenconsumed。Fromthisitisclearthatpreviouslyalso，whiletheeggwasstillroundtheyoung，thepassagesrantotheuterus。Thishappensaswehavesaidinthe’smoothhound’。
　　Intheserespectsandforthereasonsgiventhedevelopmentofcartilaginousfishesdiffersfromthatofbirds，butotherwiseittakesplaceinthesameway。Fortheyhavetheoneumbilicusinlikemannerasthatofbirdsconnectingwiththeyolk，—onlyinthesefishesitconnectswiththewholeegg（foritisnotdividedintowhiteandyolkbutallone—coloured），—andgettheirnourishmentfromthis，andasitisbeingconsumedthefleshinlikemannerencroachesuponandgrowsroundit。
　　Suchistheprocessofdevelopmentinthosefishthatproduceaperfecteggwithinthemselvesbutareexternallyviviparous。
　　4
　　Mostoftheotherfishareexternallyoviparous，alllayinganimperfecteggexceptthefrog—fish；thereasonofthisexceptionhasbeenpreviouslystated，andthereasonalsowhytheotherslayimperfecteggs。Inthesealsothedevelopmentfromtheeggrunsonthesamelinesasthatofthecartilaginousandinternallyoviparousfishes，exceptthatthegrowthisquickandfromsmallbeginningsandtheoutsideoftheeggisharder。Thegrowthoftheeggislikethatofascolex，forthoseanimalswhichproduceascolexgivebirthtoasmallthingatfirstandthisgrowsbyitselfandnotthroughanyattachmenttotheparent。Thereasonissimilartothatofthegrowthofyeast，foryeastalsogrowsgreatfromasmallbeginningasthemoresolidpartliquefiesandtheliquidisaerated。Thisiseffectedinanimalsbythenatureofthevitalheat，inyeastsbytheheatofthejuicecommingledwiththem。Theeggsthengrowofnecessitythroughthiscause（fortheyhaveinthemsuperfluousyeastymatter），butalsoforthesakeofafinalcause，foritisimpossibleforthemtoattaintheirwholegrowthintheuterusbecausetheseanimalshavesomanyeggs。Thereforearetheyverysmallwhensetfreeandgrowquickly，smallbecausetheuterusisnarrowforthemultitudeoftheeggs，andgrowingquicklythattheracemaynotperish，asitwouldifmuchofthetimerequiredforthewholedevelopmentwerespentinthisgrowth；evenasitismostofthoselaidaredestroyedbeforehatching。Hencetheclassoffishisprolific，forNaturemakesupforthedestructionbynumbers。Somefishactuallyburstbecauseofthesizeoftheeggs，asthefishcalled’belone’，foritseggsarelargeinsteadofnumerous，whatNaturehastakenawayinnumberbeingaddedinsize。
　　Somuchforthegrowthofsucheggsanditsreason。
　　5
　　Aproofthatthesefishalsoareoviparousisthefactthatevenviviparousfish，suchasthecartilaginous，arefirstinternallyoviparous，forhenceitisplainthatthewholeclassoffishesisoviparous。Where，however，bothsexesexistandtheeggsareproducedinconsequenceofimpregnation，theeggsdonotarriveatcompletionunlessthemalesprinklehismiltuponthem。Someerroneouslyassertthatallfisharefemaleexceptinthecartilaginousfishes，fortheythinkthatthefemalesoffishdifferfromwhataresupposedtobemalesonlyinthesamewayasinthoseplantswheretheonebearsfruitbuttheotherisfruitless，asoliveandoleaster，figandcaprifig。Theythinkthelikeappliestofishexceptthecartilaginous，fortheydonotdisputethesexesinthese。Andyetthereisnodifferenceinthemalesofcartilaginousfishesandthosebelongingtotheoviparousclassinrespectoftheorgansforthemilt，anditismanifestthatsemencanbesqueezedoutofmalesofbothclassesattherightseason。Thefemalealsohasauterus。Butifthewholeclasswerefemalesandsomeofthemunproductive（aswithmulesintheclassofbushy—tailedanimals），thennotonlyshouldthosewhichlayeggshaveauterusbutalsotheothers，onlytheuterusofthelattershouldbedifferentfromthatoftheformer。But，asitis，someofthemhaveorgansformiltandothershaveauterus，andthisdistinctionobtainsinallexcepttwo，theerythrinusandthechanna，someofthemhavingthemiltorgans，othersauterus。Thedifficultywhichdrivessomethinkerstothisconclusioniseasilysolvedifwelookatthefacts。Theysayquitecorrectlythatnoanimalwhichcopulatesproducesmanyyoung，forofallthosethatgeneratefromthemselvesperfectanimalsorperfecteggsnoneisprolificonthesamescaleastheoviparousfishes，forthenumberofeggsintheseisenormous。Buttheyhadoverlookedthefactthatfish—eggsdifferfromthoseofbirdsinonecircumstance。Birdsandalloviparousquadrupeds，andanyofthecartilaginousfishthatareoviparous，produceaperfectegg，anditdoesnotincreaseoutsideofthem，whereastheeggsoffishareimperfectanddosocompletetheirgrowth。Moreoverthesamethingappliestocephalopodsalsoandcrustacea，yettheseanimalsareactuallyseencopulating，fortheirunionlastsalongtime，anditisplaininthesecasesthattheoneismaleandtheotherhasauterus。Finally，itwouldbestrangeifthisdistinctiondidnotexistinthewholeclass，justasmaleandfemaleinallthevivipara。Thecauseoftheignoranceofthosewhomakethisstatementisthatthedifferencesinthecopulationandgenerationofvariousanimalsareofallkindsandnotobvious，andso，speculatingonasmallinduction，theythinkthesamemustholdgoodinallcases。
　　Soalsothosewhoassertthatconceptioninfemalefishesiscausedbytheirswallowingthesemenofthemalehavenotobservedcertainpointswhentheysaythis。Forthemaleshavetheirmiltandthefemalestheireggsataboutthesametimeofyear，andthenearerthefemaleistolayingthemoreabundantandthemoreliquidisthemiltformedinthemale。Andjustastheincreaseofthemiltinthemaleandoftheroeinthefemaletakesplaceatthesametime，soisitalsowiththeiremission，forneitherdothefemaleslayalltheireggstogether，butgradually，nordothemalesemitallthemiltatonce。Allthesefactsareinaccordancewithreason。Forjustastheclassofbirdsinsomecaseshaseggswithoutimpregnation，butfewandseldom，impregnationbeinggenerallyrequired，sowefindthesamething，thoughtoalessdegree，infish。
　　Butinbothclassesthesespontaneouseggsareinfertileunlessthemale，inthosekindswherethemaleexists，shedhisfluiduponthem。Nowinbirdsthismusttakeplacewhiletheeggsarestillwithinthemother，becausetheyareperfectwhendischarged，butinfish，becausetheeggsareimperfectandcompletetheirgrowthoutsidethemotherinallcases，thoseoutsidearepreservedbythesprinklingofthemiltoverthem，eveniftheycomeintobeingbyimpregnation，andhereitisthatthemiltofthemalesisusedup。Thereforeitcomesdowntheductsanddiminishesinquantityatthesametimeasthishappenstotheeggsofthefemales，forthemalesalwaysattendthem，sheddingtheirmiltupontheeggsastheyarelaid。Thusthentheyaremaleandfemale，andallofthemcopulate（unlessinanykindthedistinctionofsexdoesnotexist），andwithoutthesemenofthemalenosuchanimalcomesintobeing。
　　Whathelpsinthedeceptionisalsothefactthattheunionofsuchfishesisbrief，sothatitisnotobservedevenbymanyofthefishermen，fornoneofthemeverwatchesanythingofthesortforthesakeofknowledge。Neverthelesstheircopulationhasbeenseen，forfish[whenthetailpartdoesnotpreventit]copulatelikethedolphinsbythrowingthemselvesalongsideofoneanother。Butthedolphinstakelongertogetfreeagain，whereassuchfishesdosoquickly。Hence，notseeingthis，butseeingtheswallowingofthemiltandtheeggs，eventhefishermenrepeatthesamesimpletale，somuchnoisedabroad，asHerodotusthestoryteller，asiffishwereconceivedbythemother’sswallowingthemilt，—notconsideringthatthisisimpossible。Forthepassagewhichentersbywayofthemouthrunstotheintestines，nottotheuterus，andwhatgoesintotheintestinesmustbeturnedintonutriment，foritisconcocted；theuterus，however，isplainlyfullofeggs，andfromwhencedidtheyenterit？
　　6
　　Asimilarstoryistoldalsoofthegenerationofbirds。Fortherearesomewhosaythattheravenandtheibisuniteatthemouth，andamongquadrupedsthattheweaselbringsforthitsyoungbythemouth；sosayAnaxagorasandsomeoftheotherphysicists，speakingtoosuperficiallyandwithoutconsideration。Concerningthebirds，theyaredeceivedbyafalsereasoning，becausethecopulationofravensisseldomseen，buttheyareoftenseenunitingwithoneanotherwiththeirbeaks，asdoallthebirdsoftheravenfamily；
　　thisisplainwithdomesticatedjackdaws。Birdsofthepigeonkinddothesame，but，becausetheyalsoplainlycopulate，thereforetheyhavenothadthesamelegendtoldofthem。Buttheravenfamilyisnotamorous，fortheyarebirdsthatproducefewyoung，thoughthisbirdalsohasbeenseencopulatingbeforenow。Itisastrangething，however，thatthesetheoristsdonotaskthemselveshowthesemenenterstheuterusthroughtheintestine，whichalwaysconcoctswhatevercomesintoit，asthenutriment；andthesebirdshaveauteruslikeothers，andeggsarefoundthemnearthehypozoma。Andtheweaselhasauterusinlikemannertotheotherquadrupeds；bywhatpassageistheembryotogetfromittothemouth？Butthisopinionhasarisenbecausetheyoungoftheweaselareverysmalllikethoseoftheotherfissipeds，ofwhichweshallspeaklater，andbecausetheyoftencarrytheyoungaboutintheirmouths。
　　Muchdeceivedalsoarethosewhomakeafoolishstatementaboutthetrochusandthehyena。Manysaythatthehyena，andHerodorustheHeracleotsaysthatthetrochus，hastwopudenda，thoseofthemaleandofthefemale，andthatthetrochusimpregnatesitselfbutthehyenamountsandismountedinalternateyears。Thisisuntrue，forthehyenahasbeenseentohaveonlyonepudendum，therebeingnolackofopportunityforobservationinsomedistricts，buthyenashaveunderthetailalinelikethepudendumofthefemale。Bothmaleandfemalehavesuchamark，butthemalesaretakenmorefrequently；thiscasualobservationhasgivenrisetothisopinion。
　　Butenoughhasbeensaidofthis。
　　7
　　Touchingthegenerationoffish，thequestionmayberaised，whyitisthatinthecartilaginousfishneitherthefemalesareseendischargingtheireggsnorthemalestheirmilt，whereasinthenon—viviparousfishesthisisseeninbothsexes。Thereasonisthatthewholecartilaginousclassdonotproducemuchsemen，andfurtherthefemaleshavetheiruterusnearhypozoma。Forthemalesandfemalesoftheoneclassoffishdifferfromthemalesandfemalesoftheotherclassinlikemanner，forthecartilaginousarelessproductiveofsemen。Butintheoviparousfish，asthefemaleslaytheireggsonaccountoftheirnumber，sodothemalesshedtheirmiltonaccountofitsabundance。Fortheyhavemoremiltthanjustwhatisrequiredforcopulation，asNaturepreferstoexpendthemiltinhelpingtoperfecttheeggs，whenthefemalehasdepositedthem，ratherthaninformingthematfirst。Forashasbeensaidbothfurtherbackandinourrecentdiscussions，theeggsofbirdsareperfectedinternallybutthoseoffishexternally。Thelatter，indeed，resembleinawaythoseanimalswhichproduceascolex，fortheproductdischargedbythemisstillmoreimperfectthanafish’segg。Itisthemalethatbringsabouttheperfectionoftheeggbothofbirdsandoffishes，onlyintheformerinternally，astheyareperfectedinternally，andinthelatterexternally，becausetheeggisimperfectwhendeposited；buttheresultisthesameinbothcases。
　　Inbirdsthewind—eggsbecomefertile，andthosepreviouslyimpregnatedbyonekindofcockchangetheirnaturetothatofthelatercock。Andiftheeggsbebehindhandingrowth，then，ifthesamecocktreadsthehenagainafterleavingofftreadingforatime，hecausesthemtoincreasequickly，not，however，atanyperiodwhateveroftheirdevelopment，butifthetreadingtakeplacebeforetheeggchangessofarthatthewhitebeginstoseparatefromtheyolk。Butintheeggsoffishesnosuchlimitoftimehasbeenlaiddown，butthemalesshedtheirmiltquicklyuponthemtopreservethem。Thereasonisthattheseeggsarenottwo—coloured，andhencethereisnosuchlimitoftimefixedwiththemaswiththoseofbirds。
　　Thisfactiswhatweshouldexpect，forbythetimethatthewhiteandyolkareseparatedofffromoneanother，thebirdseggalreadycontainstheprinciplethatcomesfromthemaleparent……forthemalecontributestothis。
　　Wind—eggs，then，participateingenerationsofarasispossibleforthem。Thattheyshouldbeperfectedintoananimalisimpossible，forananimalrequiressense—perception；butthenutritivefacultyofthesoulispossessedbyfemalesaswellasmales，andindeedbyalllivingthings，ashasbeenoftensaid，whereforetheeggitselfisperfectonlyastheembryoofaplant，butimperfectasthatofananimal。If，then，therehadbeennomalesexintheclassofbirds，theeggwouldhavebeenproducedasitisinsomefishes，ifindeedthereisanykindoffishofsuchanatureastogeneratewithoutamale；butithasbeensaidofthembeforethatthishasnotyetbeensatisfactorilyobserved。Butasitisbothsexesexistinallbirds，sothat，consideredasaplant，theeggisperfect，butinsofarasitisnotaplantitisnotperfect，nordoesanythingelseresultfromit；forneitherhasitcomeintobeingsimplylikearealplantnorfromcopulationlikeananimal。Eggs，however，producedfromcopulationbutalreadyseparatedintowhiteandyolktakeafterthefirstcock；fortheyalreadycontainbothprinciples，whichiswhytheydonotchangeagainafterthesecondimpregnation。
　　8
　　Theyoungareproducedinthesamewayalsobythecephalopoda，e。g。
　　sepiasandthelike，andbythecrustacea，e。g。carabiandtheirkindred，forthesealsolayeggsinconsequenceofcopulation，andthemalehasoftenbeenseenunitingwiththefemale。Thereforethosewhosaythatallfisharefemaleandlayeggswithoutcopulationareplainlyspeakingunscientificallyfromthispointofviewalso。Foritisawonderfulthingtosupposethattheformeranimalslayeggsinconsequenceofcopulationandthatfishdonot；ifagaintheywereunawareofthis，itisasignofignorance。Theunionofallthesecreatureslastsaconsiderabletime，asininsects，andnaturallyso，fortheyarebloodlessandthereforeofacoldnature。
　　Inthesepiasandcalamariesorsquidstheeggsappeartobetwo，becausetheuterusisdividedandappearsdouble，butthatofthepoulpsappearstobesingle。Thereasonisthattheshapeoftheuterusinthepoulpisroundinformandspherical，thecleavagebeingobscurewhenitisfilledwitheggs。Theuterusofthecarabiisalsobifid。Alltheseanimalsalsolayanimperfecteggforthesamereasonasfishes。Inthecarabiandtheirlikethefemalesproducetheireggssoastokeepthemattachedtothemselves，whichiswhytheside—flapsofthefemalesarelargerthanthoseofthemales，toprotecttheeggs；thecephalopodalaythemawayfromthemselves。Themalesofthecephalopodasprinkletheirmiltoverthefemales，asthemalefishdoovertheeggs，anditbecomesastickyandglutinousmass，butinthecarabiandtheirlikenothingofthesorthasbeenseenorcanbenaturallyexpected，fortheeggisunderthefemaleandishard—shelled。Boththeseeggsandthoseofthecephalopodagrowafterdepositionlikethoseoffishes。
　　Thesepiawhiledevelopingisattachedtotheeggbyitsfrontpart，forherealoneisitpossible，becausethisanimalalonehasitsfrontandbackpointinginthesamedirection。ForthepositionandattitudeoftheyoungwhiledevelopingyoumustlookattheEnquiries。
　　9
　　Wehavenowspokenofthegenerationofotheranimals，thosethatwalk，fly，andswim；itremainstospeakofinsectsandtestaceaaccordingtotheplanlaiddown。Letusbeginwiththeinsects。Itwasobservedpreviouslythatsomeofthesearegeneratedbycopulation，othersspontaneously，andbesidesthisthattheyproduceascolex，andwhythisisso。Forprettymuchallcreaturesseeminacertainwaytoproduceascolexfirst，sincethemostimperfectembryoisofsuchanature；andinallanimals，eventheviviparousandthosethatlayaperfectegg，thefirstembryogrowsinsizewhilestillundifferentiatedintoparts；nowsuchisthenatureofthescolex。
　　Afterthisstagesomeoftheoviparaproducetheegginaperfectcondition，othersinanimperfect，butitisperfectedoutsideashasbeenoftenstatedoffish。Withanimalsinternallyviviparoustheembryobecomesegg—likeinacertainsenseafteritsoriginalformation，fortheliquidiscontainedinafinemembrane，justasifweshouldtakeawaytheshelloftheegg，whereforetheycalltheabortionofanembryoatthatstagean’efflux’。
　　Thoseinsectswhichgenerateatallgenerateascolex，andthosewhichcomeintobeingspontaneouslyandnotfromcopulationdosoatfirstfromaformationthisnature。Isaythattheformergenerateascolex，forwemustputdowncaterpillarsalsoandtheproductofspidersasasortofscolex。Andyetsomeevenoftheseandmanyoftheothersmaybethoughttoresembleeggsbecauseoftheirroundshape，butwemustnotjudgebyshapesnoryetbysoftnessandhardness（forwhatisproducedbysomeishard），butbythefactthatthewholeofthemischangedintothebodyofthecreatureandtheanimalisnotdevelopedfromapartofthem。Alltheseproductsthatareofthenatureofascolex，afterprogressingandacquiringtheirfullsize，becomeasortofegg，forthehuskaboutthemhardensandtheyaremotionlessduringthisperiod。Thisisplaininthescolexofbeesandwaspsandincaterpillars。Thereasonofthisisthattheirnature，becauseofitsimperfection，ovipositsasitwerebeforetherighttime，asifthescolex，whilestillgrowinginsize，wereasoftegg。Similartothisisalsowhathappenswithallotherinsectswhichcomeintobeingwithoutcopulationinwoolandothersuchmaterialsandinwater。Forallofthemafterthescolexstagebecomeimmovableandtheirintegumentdriesroundthem，andafterthisthelatterburstsandtherecomesforthasfromaneggananimalperfectedinitssecondmetamorphosis，mostofthosewhicharenotaquaticbeingwinged。
　　Anotherpointisquitenatural，whichmaywonderedatbymany。
　　Caterpillarsatfirsttakenourishment，butafterthisstagedosonolonger，butwhatiscalledbysomethechrysalisismotionless。Thesameappliestothescolexofwaspsandbees，butafterthiscomesintobeingtheso—callednymph……andhavenothingofthekind。Foraneggisalsoofsuchanaturethatwhenithasreachedperfectionitgrowsnomoreinsize，butatfirstitgrowsandreceivesnourishmentuntilitisdifferentiatedandbecomesaperfectegg。
　　Sometimesthescolexcontainsinitselfthematerialfromwhichitisnourishedandobtainssuchanadditiontoitssize，e。g。inbeesandwasps；sometimesitgetsitsnourishmentfromoutsideitself，ascaterpillarsandsomeothers。
　　Ithasthusbeenstatedwhysuchanimalsgothroughadoubledevelopmentandforwhatreasontheybecomeimmovableagainaftermoving。Andsomeofthemcomeintobeingbycopulation，likebirdsandviviparaandmostfishes，othersspontaneously，likesomeplants。
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　　Thereismuchdifficultyaboutthegenerationofbees。Ifitisreallytruethatinthecaseofsomefishesthereissuchamethodofgenerationthattheyproduceeggswithoutcopulation，thismaywellhappenalsowithbees，tojudgefromappearances。Fortheymust（1）
　　eitherbringtheyoungbroodfromelsewhere，assomesay，andifsotheyoungmusteitherbespontaneouslygeneratedorproducedbysomeotheranimal，or（2）theymustgeneratethemthemselves，or（3）theymustbringsomeandgenerateothers，forthisalsoismaintainedbysome，whosaythattheybringtheyoungofthedronesonly。Again，iftheygeneratethemitmustbeeitherwithorwithoutcopulation；iftheformer，theneither（1）eachkindmustgenerateitsownkind，or（2）someonekindmustgeneratetheothers，or（3）onekindmustunitewithanotherforthepurpose（Imeanforinstance（1）thatbeesmaybegeneratedfromtheunionofbees，dronesfromthatofdrones，andkingsfromthatofkings，or（2）thatalltheothersmaybegeneratedfromone，asfromwhatarecalledkingsandleaders，or（3）fromtheunionofdronesandbees，forsomesaythattheformeraremale，thelatterfemale，whileotherssaythatthebeesaremaleandthedronesfemale）。Butalltheseviewsareimpossibleifwereasonfirstuponthefactspeculiartobeesandsecondlyuponthosewhichapplymoregenerallytootheranimalsalso。
　　Foriftheydonotgeneratetheyoungbutbringthemfromelsewhere，thenbeesoughttocomeintobeingalso，ifthebeesdidnotcarrythemoff，intheplacesfromwhichtheoldbeescarrythegerms。Forwhy，ifnewbeescomeintoexistencewhenthegermsaretransported，shouldtheynotdosoifthegermsareleftthere？Theyoughttodosojustasmuch，whetherthegermsarespontaneouslygeneratedintheflowersorwhethersomeanimalgeneratesthem。Andifthegermswereofsomeotheranimal，thenthatanimaloughttobeproducedfromtheminsteadofbees。Again，thattheyshouldcollecthoneyisreasonable，foritistheirfood，butitisstrangethattheyshouldcollecttheyoungiftheyareneithertheirownoffspringnorfood。
　　Withwhatobjectshouldtheydoso？forallanimalsthattroublethemselvesabouttheyounglabourforwhatappearstobetheirownoffspring。
　　But，again，itisalsounreasonabletosupposethatthebeesarefemaleandthedronesmale，forNaturedoesnotgiveweaponsforfightingtoanyfemale，andwhilethedronesarestinglessallthebeeshaveasting。Noristheoppositeviewreasonable，thatthebeesaremaleandthedronesfemale，fornomalesareinthehabitofworkingfortheiroffspring，butasitisthebeesdothis。Andgenerally，sincethebroodofthedronesisfoundcomingintobeingamongthemevenifthereisnomaturedronepresent，butthatofthebeesisnotsofoundwithoutthepresenceofthekings（whichiswhysomesaythattheyoungofthedronesaloneisbroughtinfromoutside），itisplainthattheyarenotproducedfromcopulation，either（1）ofbeewithbeeordronewithdroneor（2）ofbeeswithdrones。（Thattheyshouldimportthebroodofthedronesaloneisimpossibleforthereasonsalreadygiven，andbesidesitisunreasonablethatasimilarstateofthingsshouldnotprevailwithallthethreekindsifitprevailswithone。）Then，again，itisalsoimpossiblethatthebeesthemselvesshouldbesomeofthemmaleandsomefemale，forinallkindsofanimalsthetwosexesdiffer。Besidestheywouldinthatcasegeneratetheirownkind，butasitistheirbroodisnotfoundtocomeintobeingiftheleadersarenotamongthem，asmensay。Andanargumentagainstboththeories，thattheyoungaregeneratedbyunionofthebeeswithoneanotherorwiththedrones，separatelyorwithoneanother，isthis：noneofthemhaseveryetbeenseencopulating，whereasthiswouldhaveoftenhappenedifthesexeshadexistedinthem。Itremainsthen，iftheyaregeneratedbycopulationatall，thatthekingsshallunitetogeneratethem。Butthedronesarefoundtocomeintobeingevenifnoleadersarepresent，anditisnotpossiblethatthebeesshouldeitherimporttheirbroodorthemselvesgeneratethembycopulation。
　　Itremainsthen，asappearstobethecaseincertainfishes，thatthebeesshouldgeneratethedroneswithoutcopulation，beingindeedfemaleinrespectofgenerativepower，butcontaininginthemselvesbothsexesasplantsdo。Hencealsotheyhavetheinstrumentofoffence，forweoughtnottocallthatfemaleinwhichthemalesexisnotseparated。Butifthisisfoundtobethecasewithdrones，iftheycomeintobeingwithoutcopulation，thenasitisnecessarythatthesameaccountshouldbegivenofthebeesandthekingsandthattheyalsoshouldbegeneratedwithoutcopulation。Nowifthebroodofthebeeshadbeenfoundtocomeintobeingamongthemwithoutthepresenceofthekings，itwouldnecessarilyfollowthatthebeesalsoareproducedfrombeesthemselveswithoutcopulation，butasitis，sincethoseoccupiedwiththetendanceofthesecreaturesdenythis，itremainsthatthekingsmustgenerateboththeirownkindandthebees。
　　Asbeesareapeculiarandextraordinarykindofanimalsoalsotheirgenerationappearstobepeculiar。Thatbeesshouldgeneratewithoutcopulationisathingwhichmaybeparalleledinotheranimals，butthatwhattheygenerateshouldnotbeofthesamekindispeculiartothem，fortheerythrinusgeneratesanerythrinusandthechannaachanna。Thereasonisthatbeesthemselvesarenotgeneratedlikefliesandsimilarcreatures，butfromakinddifferentindeedbutakintothem，fortheyareproducedfromtheleaders。Henceinasortofwaytheirgenerationisanalogous。Fortheleadersresemblethedronesinsizeandthebeesinpossessingasting；sothebeesareliketheminthisrespect，andthedronesareliketheminsize。Fortheremustneedsbesomeoverlappingunlessthesamekindisalwaystobeproducedfromeach；butthisisimpossible，foratthatratethewholeclasswouldconsistofleaders。
　　Thebees，then，areassimilatedtothemtheirpowerofgeneration，thedronesinsize；ifthelatterhadhadastingalsotheywouldhavebeenleaders，butasitisthismuchofthedifficultyhasbeensolved，fortheleadersarelikebothkindsatonce，likethebeesinpossessingasting，likethedronesinsize。
　　Buttheleadersalsomustbegeneratedfromsomething。Sinceitisneitherfromthebeesnorfromthedrones，itmustbefromtheirownkind。Thegrubsofthekingsareproducedlastandarenotmanyinnumber。
　　Thuswhathappensisthis：theleadersgeneratetheirownkindbutalsoanotherkind，thatofthebees；thebeesagaingenerateanotherkind，thedrones，butdonotalsogeneratetheirownkind，butthishasbeendeniedthem。AndsincewhatisaccordingtoNatureisalwaysindueorder，thereforeitisnecessarythatitshouldbedeniedtothedroneseventogenerateanotherkindthanthemselves。
　　Thisisjustwhatwefindhappening，forthoughthedronesarethemselvesgenerated，theygeneratenothingelse，buttheprocessreachesitslimitinthethirdstage。AndsobeautifullyisthisarrangedbyNaturethatthethreekindsalwayscontinueinexistenceandnoneofthemfails，thoughtheydonotallgenerate。
　　Anotherfactisalsonatural，thatinfineseasonsmuchhoneyiscollectedandmanydronesareproducedbutinrainyreasonsalargebroodofordinarybees。Forthewetcausesmoreresidualmattertobeformedinthebodiesoftheleaders，thefineweatherinthatofthebees，forbeingsmallerinsizetheyneedthefineweathermorethanthekingsdo。Itisrightalsothatthekings，beingasitweremadewithaviewtoproducingyoung，shouldremainwithin，freedfromthelabourofprocuringnecessaries，andalsothattheyshouldbeofaconsiderablesize，theirbodiesbeing，asitwere，constitutedwithaviewtobearingyoung，andthatthedronesshouldbeidleashavingnoweapontofightforthefoodandbecauseoftheslownessoftheirbodies。Butthebeesareintermediateinsizebetweenthetwootherkinds，forthisisusefulfortheirwork，andtheyareworkersashavingtosupportnotonlytheiryoungbutalsotheirfathers。