WHALES, rORPOISES, AND DOLPHINS. 171 



and some of them are comparatively small creatures, the cetacean order 

 includes not only the largest of all mammals, but likewise of all living 

 animals. That they trace their origin back to terrestrial mammals may be 

 considered beyond all doubt, although from what particular group they are 

 descended cannot at present be determined. As a rule, the various pelagic 

 representatives' of the order enjoy a very wide geographical range, although 

 certain species, such as the Greenland-whale of the Arctic Ocean, and the 

 pigmy-whale of the Southern Seas, are coniiiied to a relatively small area. 

 Almost all cetaceans are carnivorous. 



Cetaceans are divisible into two great divisions, or sub-orders, known aa 

 the whalebone-whales (Mystacoceti), and the toothed whales {Odontoceti) ; the 

 former group comprising only the single family {BaUenidcE), 

 whereas the latter ia divided into three families. As their Whalebone- 

 names imply, the most obvious distinction between these two Whales, 

 groups relates to the absence or presence of functional teeth ; 

 the absence of teeth in the first group being compensated by the develop- 

 ment of the peculiar substance known as whalebone, or baleen. In the 

 young of the whalebone-whales, rudiments of true teeth are, however, 

 developed beneath the roots of the incipient whalebone, although these sub- 

 sequently wither without having ever cut tne gum. As the nature and struc- 

 ture of whalebone is a matter of some interest and importance, a small space 

 must be devoted to its consideration before entering upon the leading charac- 

 teristics of the Mystacoceti. Whalebone, then, is a horny substance attached 

 to the roof of the mouth, from which it hangs by a broad, transversely-arched 

 base, in the form of a series of parallel, narrow, elongated triangular plates, 

 placed transversely to the long axis of the mouth, with their external edtjes 

 firm and straight, but the inner ones frayed out into a kind of fringe. The 

 longest plates of whalebone are situated near the middle of the jaw, from 

 which point the length gradually diminishes towards the two extremities, 

 where they become very short. Whereas, however, in the Greenland-whale 

 the length of the longest plates variea from some 10 to 12 ft., and the total 

 number of plates in the series is about 380, in the great rorquals or fin-whales, 

 the length is only a few inches, while the number of plates is considerably 

 less. To accommodate the enormous whalebone-plates of the Greenland- 

 whale, the bones of the upper jaw are greatly arched upwards, and the 

 slender lower jaw is bowed outwards, thus leaving a large space — both in the 

 vertical and horizontal directions — the transverse diameter of which is much 

 wider below than above. When the mouth is closed, the plates of whalebone 

 are folded obhquely backwards, with the front ones lying beneath those be- 

 hind them ; but directly the jaws are opened, the elastic nature of this 

 substance causes it to spring at once into a vertical position, and thus form a 

 sieve-like wall on both sides of the mouth, the thin enas of the plates being 

 prevented from pushing outwards by the stiff lower lip which overlaps them. 

 By elevating its enormous fleshy tongue within the cavity thus formed, the 

 whale causes the enclosed water to rush out between the plates, leaving such 

 small creatures as it contained lying dry on the surface of the tonyue ready 

 for swallowing. In structure, whalebone, which, although black in the 

 Greenland-whale, is white in some of the other species, is of a horny nature, 

 and grows from transverse ridges on the mucous membrane of the roof of 

 the mouth; being, in fact, nothing more than an extreme development of 

 the ridges on the palate of a cow, hardened and lengthened by an excessive 

 growth of a horny superficial or epithelial layer. The whole of this vast 



