BRIEF SKETCH OF THE TOOTHED WHALES. 83 



as the large forms are included as a group of mammals, are 

 readily distinguished by their wholly aquatic existence, the only 

 other mammals having a similar habit being the Sirenians, viz. 

 the Manatees and Dugongs, which, however, diverge consider- 

 ably in structure from the whales. So truly aquatic are the 

 Cetaceans that deposition on land is usually fatal, and therefore 

 they materially differ from such as the seals, which frequently 

 leave the water of their own accord and bask on the rocks and 

 sand. An exception, however, was the Galifornian Grey Whale 

 {Rhachionectes glaucus), which was often found amidst the surf. 

 This interesting species is said to be now exterminated by the 

 persistent pursuit of man. While thus they resemble the fishes 

 in being confined throughout their existence to the water, they 

 are as characteristically mammalian in structure as the most 

 typical member of that class, though it is true their framework 

 as well as their various organs are modified to suit their aquatic 

 life, and some parts are absent or rudimentary. 



In the form of the body the Cetacean is fish-like, being 

 spindle-shaped or club-shaped in outline, without a definite 

 neck, though in one or two a trace exists, tapered more pos- 

 teriorly than anteriorly, and having a powerful tail composed 

 of two divisions or "flukes," placed horizontally, and thus 

 differing from the vertical tail of all fishes and the gigantic 

 Ichthyosaurians. The body is covered with the mammalian 

 skin, the surface or cuticle being smooth, and with compara- 

 tively few hairs, so characteristic of other mammals. This 

 scarcity of hairs might at first sight be considered a most 

 exceptional feature, since one of the leading characters of 

 mammals is the presence of such a covering. A closer scrutiny, 

 however, shows that hairs are by no means absent in the 

 whales. Thus, for instance, the newly born Eight or Whale- 

 bone Whale has numerous bristles on the upper and lower lips* 

 and near the blow-holes. Moreover, Mr. Lilliet has recently 

 shown that in the adult examples of Balcenoptera muscidus and 

 B. sibbaldii a definite distribution of hairs could be made out in 

 the shape of four rows of straight, white, bristle-like hairs on 



* Sixty-six near extremity of upper jaw; about fifty on each side of 

 lower lip ; a few near blow-holes. 



f Proc. Zool. Soc. 1910, p. 773, with text-figs., May, 1910. 



Ef2 



