From cleavage to primitive streak formation: A complementary normal table and a new look at the first stages of the development of the chick: I. General morphology

[摘要] Amanualmethodhasbeendevelopedtoextracteggsfromthegenitaltractwithoutharmingthehen.FourteendevelopmentalstagesprecedingHamburgerandHamilton'sstage2havebeenstudiedfromlivematerialandphotographedfrombothupperandlowersurfaces.Threedevelopmentalperiodshavebeendistinguished:cleavage,formationofareapellucida,andhypoblastformation.Thelasttwoaremorphogeneticperiodswhichfollowthedeterminationoftheembryonicaxis.Duringcleavagethediameterofthegermbecomesreducedandthecytoplasmicmassbecomesthicker.Laterthereisaprogressiveincreaseofthegerm'sarea.Theformationoftheareapellucidaisaresultofanorientedmassivelossoftheyolkladencellsofthelowerlayers.Theformationoftheprimaryhypoblastisaresultofposterio-anteriorlyorientedpolyinvaginationandalatercoalescenceofthecellaggregatesinthesamedirection.Itisnotyetpossibletoconcludewhetherthereisalsoananteriorlydirectedcellmovement.Theinconsistentusageofthetermsblastodiscandblastodermisdiscussed.Theauthorssuggestavoidingthetermblastodiscandusingthegeneraltermgermforalltheearlystages.ThetermblastodermmaybeappliedfromstageVIonward.

[学科分类] 生物科学（综合）