WHALES, PORPOISES, AND DOLPHINS. 175 



The Australians interested in the success of the trade are confident that a 

 large industry in whale and seal-fishing could be developed in the Antarctic 

 seas by auxiliary screw-whalers, which could be fitted out at the comparatively 

 small cost of £6000 each. 



The essential characteristic of the toothed-whales, or Odontoceti, ia a 

 negative one, and consists in the entire absence of whalebone. Very generally, 

 indeed, teeth- are developed, at least in the lower jaw, bub 

 these may be reduced to a sinole pair, or even in the male Toothed Whales, 

 narwhal to a solitary tooth, while in the female of the latter 

 species there are none of any functional importance. Another very well- 

 marked point of distinction is the single external aperture of the nostrils, 

 which very frequently takes the form of a transverse crescentic slit, closed by 

 a flap-like valve. Then, again, the skull is always more or less unsymmetrical 

 in the region of the nostrils, and in the existing members of the sub-order the 

 nasal bones are reduced to mere rounded nodules, taking no share in roofing 

 the nasal cavity. In certain extinct forms, however, these bones are of more 

 normal character, and partially cover the chamber of the nose. No trace of 

 an organ of smell is retained by any of the toothed-whales. In the skeleton 

 the breast-bone, or sternum, is usually composed of several distinct portions, 

 to which the extremities of several of the ribs are articulated by the interven- 

 tion of cartilages ; and a certain number of the anterior ribs are articulated at 

 their upper ends to the bodies of the vertebrfe, as well as to the transverse 

 processes of the same. The lower jaw of a toothed-whale may always be 

 distinguished from that of a whalebone-whale by the two branches being 

 nearly straight, of great depth at the hinder extremity, and in front uniting 

 with one another by a bony union of larger or smaller extent. In all the 

 members of the group the skeleton of the flippers exhibits five complete 

 digits. Throughout the sub-order the teeth are always of a simple structure, 

 having conical or compressed crowns and undivided roots ; and only a single 

 series is ever developed, the replacement of the anterior teeth, so common 

 among mammals, being wanting. In number the teeth of many species greatly 

 exceed the ordinary mammalian series. Observations on fcetal cetaceans 

 have indeed shown that rudiments of a second series of teeth are developed 

 in the gums, which serve to show that the functional teeth correspond in the 

 main to the milk-series of ordinary mammals. 



Although in the development of whalebone and the loose articulation of the 

 ribs to the backbone the whalebone-whales are clearly more specialised than 

 the toothed- whales, yet as regards the single nostril and the structure of the 

 nasal bones the latter group is decidedly more aberrant than the former. 

 Hence it may be inferred that neither of the two sub-orders is derived from 

 the other, but that both have grown up side by side quite independently. 

 It has generally been considered that they are divergent branches from a 

 common ancestral stock ; but it is possible that they have no sort of genetic 

 affinity with each other, and have respectively originated from two totally 

 distinct mammalian groups. More decisive evidence than any yet adduced 

 is, however, required before the latter view can be definitely accepted. 



The largest of all the toothed- whales is the gigantic sperm-whale (Physeter 

 macrocephalus), the sole member of its genus, and the typical representative 

 of a family {Physeteridce) characterised by the absence of teeth in the upper 

 jaw of the adult, and the variability, both as regards size and number, of those 

 of the lower jaw. In all the members of the family the hinder portion of the 

 skull is much elevated, so as to form either a semi-circular wall, or a pair of 



