THE 



ANATOMY OF VERTEBRATES. 



CHAPTER I. 



CHARACTERS OF VERTEBRATES. 



1. Developmental characters. Vertebrates, like lower animals, 

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

 a ; primarily differentiating into albumen, fibrine, lemma, ib. , c l , 

 nuclei and cells ; in winch 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 f yolk,' fig. 1, 

 B,C ; the germinal vesicle may 

 be obscured by endogenous 

 multiplication of granules, 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 hyaline nucleus or 



* Stages of derelopement of the ovarian egg of a vertebrate 



prodllCt Of the Sperm-Cell, fig. animal (Gasterosteus). CLXXVI. 



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



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



1 Gr. lemma, skin ; also called 'primary' or 'basement' membrane ; distinguished, 

 through its relations, as * ncurilemma, sarcolemma, adcnolemma ' or the limitary 

 membrane of gland-follicles, c. 



