212 WHALES, PAST AND PRESENT xv 



absolutely isolated, and little satisfactory reason has ever been 

 given for deriving them from any one of the existing divisions 

 of the class rather than from any other. The question has 

 indeed often been mooted whether they have been derived 

 from land mammals at all, or whether they may not be the 

 survivors of a primitive aquatic form which was the ancestor 

 not only of the whales, but of all the other members of the 

 class. The materials for I will not say solving but for 

 throwing some light upon this problem, must be sought for 

 in two directions in the structure of the existing members 

 of the order, and in its past history, as revealed by the 

 discovery of fossil remains. In the present state of science 

 it is chiefly on the former that we have to rely, and this 

 therefore will first occupy our attention. 



One of the most obvious external characteristics by 

 which the mammalia are distinguished from other classes of 

 vertebrates is the more or less complete clothing of the 

 surface by the peculiar modification of epidermic tissue called 

 hair. The Cetacea alone appear to be exceptions to this 

 generalisation. Their smooth, glistening exterior is, in the 

 greater number of species, at all events in adult life, absolutely 

 bare, though the want of a hairy covering is compensated for 

 functionally by peculiar modifications of the structure of the 

 skin itself, the epidermis being greatly thickened, and a 

 remarkable layer of dense fat being closely incorporated with 

 the tissue of the derm or true skin ; modifications admirably 

 adapted for retaining the warmth of the body, without any 

 roughness of surface which might occasion friction and so 

 interfere with perfect facility of gliding through the water. 

 Close examination, however, shows that the mammalian 

 character of hairiness is not entirely wanting in the Cetacea, 

 although it is reduced to a most rudimentary and apparently 

 functionless condition. Scattered, small, and generally delicate 

 hairs have been detected in many species, both of the toothed 

 and of the whalebone whales, but never in any situation but 

 on the face, either in a row along the upper lip, around the 

 blowholes or on the chin, apparently representing the large, 

 stiff " vibrissse " or " whiskers " found in corresponding situa- 

 tions in many land mammals. In some cases these seem to 



