xiv INTR OD UCTOR Y 



definition would be classified by the author of that 

 dictionary as a fish. To the naturalist the remark- 

 able adaptation to its mode of life with the resultant 

 fish-like form is no less interesting. But no com- 

 petent zoologist has any longer any doubt of the 

 mammalian character of the Cetacea. It is even 

 possible to assert that whales are remote from some 

 of the existing and vanished groups of mammals, 

 but the exact affinities of these creatures is a matter 

 which is still disputed ; there is thus a field for 

 speculation which at present has hardly any limits. 

 In cases of this kind new and important evidence 

 may be forthcoming at any minute, which lends a 

 particular fascination to the study of this group, 

 much more than to the study of those groups whose 

 affinities are more thoroughly known. The existing 

 knowledge of this group is very far from being 

 complete. From the nature of the case whales are 

 exceedingly difficult to investigate. The opportuni- 

 ties for dissection are practically confined to stranded 

 specimens, and the stranding of whales is not an 

 every-day occurrence. Obvious difficulties, moreover, 

 hamper the naturalist who is so fortunate as to receive 

 timely information of the stranding of a desirable 

 specimen. On the other hand, there is much more 

 accumulated knowledge concerning the skeleton of 

 the Cetacea ; but even here there are many regret- 

 table lacunae, not only by reason of the frequent 

 imperfections of the skeletons, but also by sheer lack 



