362 Professor Flower [May 25, 



tinguishes a mammal from one of the oviparous vertebrates, whether 

 in the osseous, nervous, vascular, or reiDroductive systems, they are as 

 truly mammalian as any, even the highest, members of the class. 

 Any supposed signs of inferiority are, as we shall see, simply modifi- 

 cations in adaptation to their peculiar mode of life. Similar modifica- 

 tions are met with in another quite distinct group of mammalia, the 

 Sirenia (Dugongs and Manatees), and also, though in a less complete 

 degree, in the aquatic Carnivora or seals. But these do not indicate 

 any community of origin between these groups and the Cetacea. 

 In fact, in the present state of our knowledge, the Cetacea are 

 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 regions — 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 occu^^y 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 modifi- 

 cation of epidermic tissue called hair. The Cetacea alone appear to 

 be exceptions to this generalisation. Their smooth, glistening exte- 

 rior 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. Scat- 

 tered, 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 "vibrissas" or "whiskers" found in corresponding situa- 

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

 throughout the life of the animal ; more often they are only found in 

 the young or even the foetal state. In some species they have not 

 been detected at any age. 



