88 THE GENESIS OF SPECIES. [CHAP. 



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

 tion. 10 



Nevertheless, in the two-gilled Cephalopods (Dibran- 

 chiata) we find the brain supported and protected 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 



CUTTLE-FISH. 

 A. Ventral aspect. B. Dorsal aspect. 



the cerebral ganglia into the cartilaginous chambers 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 the first 

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

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



10 This remark is made without prejudice to possible affinities in the 

 direction of the Ascidians an affinity which, if real, would be irrelevant 

 to the question here discussed. 



