EVOLUTION OF THE VERTEBRATA. 329 



tebrae are of the protocercal type. As this group does not appear 

 early in geological time, and as it is largely represented now in 

 the abyssal ocean fauna, there is every reason to regard it as a 

 degenerate type.* The 

 scyphobranch line presents 

 a specialization of the su- 

 perior pharyngeal bones, 

 which is continued by the 

 Haplodoci (Batrachids). 

 This can not be called a 

 degenerate line, although 

 the fin-rays are soft. The 

 Heterosomata (flounders) 

 found it convenient to lie 

 on one side, a habit which 

 would appear to result 

 from a want of motive en- 

 erg}'. The fins are very 

 inefficient organs of move- 

 ment in them, and they 

 are certainly no rivals for 

 swift-swimming fishes in 

 the struggle for existence, 

 excepting as they conceal 

 themselves. In order to 

 see the better while un- 

 seen, the inferior eve has ■§ a o ^ g § 

 turned inward, i. e., up- | § J /fl J K 

 ward, and finally has pen- *^ rh cu / i>-^ 

 etrated to the superior 

 surface, so that both eyes 

 are on one side. This pe- 

 culiarity would be incred- 

 ible if we did not know 

 of its existence, and is an 

 illustration of the extraordinary powers of accommodation pos- 



O 

 O 



* The general characters of the deep-sea fish-fauna are those of degeneracy. 

 (Ed. 1886.) 



f This order was proposed by Gill for the Eurypharyngidae, and is now added. 

 (Ed. 1886.) 



