VI.] SPECIES AND TIME. 159 



highly organized sharks and rays) and the Ganoids, a 

 group now poorly represented, but for which the sturgeon 

 may stand as a type, and which in many important re- 

 spects more nearly resemble higher Vertebrata than do the 

 ordinary or osseous fishes. Fishes in which the ventral 

 fins are placed in front of the pectoral ones (i.e. jugular 

 fishes) have been generally considered to be comparatively 

 modern forms. But Professor Huxley has obligingly in- 

 formed the author that he has discovered a jugular fish in 

 the Permian deposits. 



Amongst the molluscous animals we have members of 

 the very highest known class, namely, the Cephalopods, or 

 cuttle-fish class ; and amongst articulated animals we find 

 Trilobites and Eurypterida, which do not belong to any 

 incipient worm-like group, but are distinctly differentiated 

 Crustacea of no low form. 1 



We have in all these animal types nervous systems dif- 

 ferentiated on distinctly different patterns ; fully formed 

 organs of circulation, digestion, excretion, and generation ; 

 complexly constructed eyes and other sense organs. In 

 fact we have all the most elaborate and complete animal 

 structures built up, and not only once ; for in the fishes 

 and mollusca we have (as described in the third chapter 

 of this work) the coincidence of the independently de- 

 veloped organs of sense attaining a nearly similar com- 

 plexity in two quite distinct forms. If, then, so small an 

 advance in organization has been made in fishes, molluscs, 



1 Dr. Scndder " lias lately found a fossil insect in the Devonian for- 

 mation of New Brunswick, which is furnished with the well-known 

 tympanum or stridulating apparatus of the male Locustidse. " (Trans. 

 Ent. Soc., Third Series, vol. ii., quoted in Darwin's "Descent of Man," 

 vol. i. p. 360.) 



