60 TOOTHED WHALES AND THEIK ANCESTKY. 



shaped crowns were furnished with a number of cusps on 

 their hinder cutting-edges. Indeed, these teeth much 

 resemble the premolar teeth of a dog or the molars of a 

 seal ; and they obviously serve to indicate a transition from 

 the modern toothed cetaceans towards ordinary mammals. 

 This, however, is by no means all, since in a still earlier 

 portion of the same division of the Tertiary period there 

 occur other cetacean-like animals known as zeuglodonts, 

 which have still more complicated teeth, and otherwise 

 depart further from the modern cetacean type — so much so, 

 indeed, that they have been regarded by some writers as 

 more nearly allied to the seals. In our own ojjinion they are, 

 however, undoubtedly primitive cetaceans, and thus serve, 

 not only to connect the present group with other mammals, 

 but also, in conjunction with the shark-toothed dolphins, to 

 show that the simple teeth of the former are clearly pro- 

 duced by degeneration from a complex type. As regards 

 the particular group of land mammals from which whales 

 were derived, it has been thought that their nearest allies 

 are with the ancestors of the pig-like hoofed mammals. 

 This, indeed, is the view of Sir W. H. Flower ; but we 

 confess that from the nature of the teeth of the two extinct 

 groups above mentioned, coupled with certain resemblances 

 of the skeleton of the zeuglodonts to those of seals, we 

 are rather more inclined to look among flesh-eating land 

 mammals for the lost ancestors. Still, however, it must 

 be remembered that in the early Eocene period, which is 

 probably the very latest epoch at which cetaceans could 

 have originated, the distiuctioa between carnivorous and 

 hoofed mammals was but imperfect, so that, after all, the 

 ancestral cetacean stock may well have been of an 

 extremely generalized type. At present, however, we are 

 almost completely in the dark in all that concerns this 

 interesting subject. 



By far the largest of all the toothed whales is the 

 gigantic sperm-whale, the typical representative of a family 

 characterized by the absence of teeth in the upper jaw of 

 the adult, while those of the lower jaw are very variable 

 both as regards form and number. In the sperm-whale, of 

 which the male attains a length of between fifty and sixty 



