230 CETACEA 



reptiles, birds, and mammals, the Whale resembles the last-named 

 and differs from the fish. It is as essentially a mammal as a Cow 

 or a Horse, and simply resembles a fish externally because it is 

 adapted to inhabit the same element ; but it is no more on that 

 account a fish than is a bat, because adapted to pass a great part of 

 its existence on the wing in the air, nearly related to a bird. The 

 whole structure of a whale is a most instructive instance of a type 

 of organisation which is common to and characteristic of the class 

 Mammalia, but specially modified or adapted to a peculiar mode of 

 life. We see in every part the result of two great principles acting 

 and reacting upon each other on the one hand, adherence to type, 

 or rather to fundamental inherited structural conditions, and, on 

 the other, adaptation to the peculiar circumstances under which it 

 lives, and to which in all probability it Has become gradually more 

 and more fitted. The external fish-like form is perfectly suited for 

 swimming through the water; the tail, however, is not placed 

 vertically as in fishes, but horizontally, a position which accords 

 better with the constant necessity for rising to the surface for the 

 purpose of breathing. The hairy covering characteristic of all 

 mammals, which if present might interfere with rapidity of move- 

 ment through the water, is reduced to the merest rudiments a 

 few short bristles about the chin or upper lip which are often 

 only present in very young animals ; and the function of keeping 

 the body warm is supplied by the "blubber." The fore -limbs, 

 though functionally reduced to mere paddles, with no power of 

 motion except at the shoulder-joint, have beneath their smooth and 

 continuous external covering all the bones, joints, and even most of 

 the muscles, nerves, and arteries of the human arm and hand ; and 

 the rudiments of hind legs found buried deep in the interior of the 

 animal apparently subserve no useful purpose, but point an in- 

 structive lesson to those who are able to read it. 



As before said, the Cetacea form a perfectly well-defined group, 

 sharply separated from all other mammals, and with no outlying or 

 doubtful forms at present known. Among the existing members 

 of the order, there are two very distinct types, the Toothed Whales 

 or Odontoceti and the Baleen Whales or Mystacoceti, which present 

 as many marked distinguishing structural characters as are found 

 between many other divisions of the Mammalia which are reckoned 

 as orders. The extinct Zeuglodon, so far as its characters are known, 

 does not fall into either of these groups, but is in some respects an 

 annectant form, and therefore must be placed, provisionally at least, 

 in a third group by itself. 



The Mystacocetes appear at first sight to be the most specialised 

 and aberrant of the existing Cetacea, as indicated by the absence of 

 teeth, the presence of baleen, and the form and size of the mouth ; 

 but, as we see in other groups, dental characters, and all such as 



