THE 



ANATOMY OF VERTEBRATES. 



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CHAPTER I. 



CHARACTERS OF VERTEBRATES. 



§ 1. Developmental characters. — Vertebrates, like lower animals, 

 begin in a semifluid nitrogenous substance called ' plasma,' fig. 1 , A, 

 rt ; primarily differentiating into albumen, fibrine, lemma, ib. b, c^, 

 nuclei and cells ; in which lat- 

 ter form the individuality of 

 the new organism first dawns 

 as a nucleated ' germ-cell ' or 

 germinal vesicle, ib. d. 



By the evolution of albumi- 

 nous granules and oil-particles 

 plasma becomes ' yolk,' fig. 1, 

 B, C ; the germinal vesicle may 

 be obscured by endogenous 

 multiplication of granul es, gra- 

 nular cells and oil-globules, 

 which combine with those of 

 the yolk to form its germinal 

 part : an outer layer of ' lem- 

 ma,' D, ch, completes the un- 

 impregnated vertebrate egg. 



For further developement 

 another principle is needed, 



VIZ. the hyahne nucleus or sta„pgo((,„y|,iopement.oftbeovarianegKofa\-ei-tebralc 



product of the sperm-cell, fig. ™™'" (e<»*™»*"'^)- oi-xxvi. 



2, called ' spermatozoon.' Its reception by the egg, as at a, b, fig. 



3, is followed by the formation of a germ-mass. This mass is due 



' Gr. krnma, skin ; also called 'primary' or Miasemcnt' membrane ; distinguished, 

 through its relations, as ' iienrilemraa, sarcolcmraa, adcnolerauia' or the limitary 

 membrane of gland-follicles, &c. 



