2 CETACEANS. 
external surroundings, and have no sort of connection with their affinities. The 
fish-like resemblances of the Cetaceans are, moreover, not so close as they may at 
first sight appear; since the tail-fin, instead of being vertical, is horizontal, while 
the structure of the skeleton of the fore-lmb is totally different from that of any 
fish. The general fish-like form of the body is, however, that best adapted for 
progression through the water, which affords sufficient reason for its having been 
acquired in the present group of animals; and we may likewise mention that 
Cetaceans generally resemble fish in having the upper-part of the body coloured 
dark, while the under-parts are light, such a coloration rendering the animals in 
which it occurs not easily seen, either from above or below, when in their native 
element. 
Wo Connection That whales are not even directly descended from fishes is 
with Fishes. evident from the fact of their breathing atmospheric air, by means 
of lungs, for if they had so originated it would be quite clear that they would have 

SKELETON OF GREENLAND WHALE, 
retained fish-like gills, and thus have avoided the necessity of coming periodically 
to the surface for the purpose of breathing. It is probably for this reason that 
Cetaceans have their tails with the expansion placed in a horizontal instead of a 
vertical plane, since the strokes of such a horizontally-expanded organ are the best 
calculated to bring an animal rapidly to the surface. 
The additional circumstance that Cetaceans retain traces of the 
hairy covering, which is so characteristic of mammals in general, 
affords evidence that they derive their origin from terrestrial mammals; and, 
taken together with the absence of hind-limbs, is amply sufficient to disprove 
any notion that they themselves are in any sort of way connected with the 
ancestral stock from which the other members of the class have originated. 
Cetaceans may, therefore, be regarded as some of the most specialised of all 
mammals. With regard to the terrestrial mammals to which these animals are 
most closely related, there is still great uncertainty and some difference of opinion 
among zoologists. Sir W. H. Flower is inclined to consider that they show more 
resemblances to Ungulates, and especially the Even-toed group ; but the teeth of the 
earliest forms are quite unlike those of any Ungulates, and approximate much more 
closely to those of Carnivores. It may, therefore, be suggested that the alliance 
between Cetaceans and Carnivores may prove to be closer than is often considered 
DSI 
Origin. 
