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 gerni- 

 layer (mesoderm), and 



Pig. 385.— Placoid scale of dog-fish (vertical sec- ;„ ii... „„,,,„ tl-,o mnQfloa 

 tion magnified), o, enamel layer ; b, dentine of the ^H ^IC gei m tne mUSCleS 

 spine on the scale.-After Owen. Jj^ p^j,^ j^^.JgQ f ^qjj^ ^J^g 



primary segments indicated by the protoyertebrfe, 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 

 bauds, which corre- 

 spond in number to 

 the vertebrfe (Gegen- 

 baur). 



The eye in Verte- 

 brates in its develop- 

 mentalhistory belongs 

 to a different type of 

 structure from that of 



any invertebrates, Un pi^. gge.^cyloid scale of roach, magnified, seen in 

 less it be the larval section, ^, and from the surface, B.— After Owen. 



Ascidians, for in both tyjoes tlie eye is said by Gegenbaur not 

 to be directly developed from the ectoderm, but from the 



