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- -1 o-prm thp muscles 

 tion magnified). , enamel layer ; 6, dentine of the ln me g el 

 spine on the scale. After Owen. J n p ar t arise from, the 



primary segments indicated by the protovertebrse, 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- 

 mental history belongs 

 to a different type of 

 structure from that of 



any invertebrates, Ull -pig. 386.-Cyloid scale of roach, magnified, seen iii 

 less it be the larval section, ^, and from the surface, ^.-AfterOwen. 



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

 to be directly developed from the ectoderm, but from the 



