384 



ZOOLOGY. 



The head of the sturgeon, garpike, and of other ganoid 

 fishes, is protected by solid dermal bones, and the shells of 

 turtles are dermal structures. 



The color of the skin of Vertebrates is due to pigment- 

 granules situated either in the epidermis or dermis, and in 



the chameleon they 

 are contained in special 

 sacs (chromatophores) 

 which are under the 

 control of the nervous 

 system. 



The muscvilar system 

 of Vertebrates arises 

 from the middle germ- 

 layer (mesoderm), and 



Mg. 385.— Placoid scale of dog-fish (vertical eec- ■ '\t l-i i 



tion magiufled). o, enamel layer ; *, deutinc of tlie in 1-^6 germ tllG mUSCleS 

 spine on the scale-Altci- Owen. jj^ ^^^.f. ^^.^^^ ^^.^^ ^j^^, 



primary segments indicated by the protovertebrfe, while iix 

 the adults of fishes and certain salamanders, the muscular 

 system is distinctly segmented, corresponding to the seg- 

 mentation of the ver- 

 tebral column, the 

 four lateral trunk- 

 muscles being divided 

 into a number of seg- 

 ments by tendinous 

 bands, which corre- 

 spond in number to 

 the vertebrae (Gegen- 

 baur). 



The eye in Verte- 

 brates in its develop- 

 mentalhistorybelongs 

 to a different type of 

 structure from that of 

 any invertebrates, un 

 less it be the larval 



Pie. 386.-C3;loid scale of roach, maKulfied, seen in. 

 section, A, and from the surface, .B.— After Owen. 



Ascidians, for in both types the eye is said by Gegenbaur not. 

 to be directly developed from the ectoderm, but from the- 



