404 



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 muscular system 

 of Vertebrates arises 

 from the middle germ- 

 layer (mesoderm), and 



Fig. 385. Placoid scale of dog-fish (vertical sec- 41. .. _._- i.\^ n Yvmo/Vloc. 

 tiqn magnified). a, enamel layer ; 6, dentine of the m "-he germ the muscles 

 spine on the scale.-After Owen. j n p art a ^ ge f rom ^e 



primary segments indicated by the protovertebrae, while in 



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, im 

 less it be the larval 



-CyHM scale of roach, magnified, seen in 

 > and from tne 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 



