INTRO D UCTOR Y xv 



of material in the case of many forms, particularly 

 among the dolphins. The often fragmentary char- 

 acter of the available Cetacean remains, and the 

 consequent and necessary inability to distinguish 

 between what might be fairly regarded as real 

 specific or generic differences and what were mere 

 variations, led the late Dr. Gray to create a vast 

 number of species and genera of whales ; compara- 

 tively few of those new forms which he instituted 

 are now allowed by the students of this group. 

 Though doubtless a good many forms remain for 

 identification and establishment, the total number of 

 real species and genera of whales is a comparatively 

 small one. This is itself an inducement to the study 

 of the order, since it is possible to acquire a general 

 knowledge of the whole group. The naturalist who- 

 hopes to have a thorough acquaintance with such 

 an order as that of the Rodentia has much work 

 before him. The student of the Cetacea, on the 

 other hand, has to deal with not more than thirty- 

 five genera and at most eighty species. It will be 

 attempted to give the bulk of what is known con- 

 cerning all of these in the present volume. 



