88 



THE GENESIS OF SPECIES. 



[Chap. 



yet been discovered, eitljer living or in a fossilized condi- 

 tion.'" 



Nevertheless, in the two-gilled Cephalopods {JDibran- 

 cJiiata) we iind the bruin supported and i)rotected by a car- 

 tilaginous cranium. In the base of this cranium are two 

 cartilaginous chambers. In each chamber is a membranous 

 sac containing an otolith, and the auditory nerves pass from 



B 



CPTTLE-FISn. 



A. Ventral aspect. B. Dorsal aspect. 



the cerebral ganglia into the cartilaginous cliambers to reach 

 the auditory sacs. Moreover, it has been suggested by 

 Prof. Owen that sinuosities between processes projecting 

 from the inner wall of each chamber "seem to be tiie hrst 

 rudiments of those which, in the higher classes (i. e., in 

 animals with a sjiinal column), are extended in the form of 



"^ Tills remark is niade witliout prejudice to possible aninities in the 

 direetion of the Ascidians — an allinity which, if real, would be irrelevant 

 to the question liere discussed. 



