206 THE POPULAR SCIENCE MONTHLY. 



the thighs and legs are small, the feet are large and are the special 

 organs of locomotion in the water, the tail being quite rudimentary. 

 In the whales the hind-limbs are aborted and the tail developed into a 

 powerful swimming organ. Now, it is very difficult to suppose that, 

 when the hind-limbs had once become so well adapted to a function 

 so essential to the welfare of the animal as that of swimming, they 

 could ever have become reduced and their action transferred to the 

 tail. It is far more reasonable to suppose that whales were derived 

 from animals with large tails, which were used in swimming, event- 

 ually with such effect that the hind-limbs became no longer neces- 

 sary, and so gradually disappeared. The powerful tail, with lateral 

 cutaneous flanges, of an American species of otter {Pteronura sand- 

 bachii), or the still more familiar tail of the beaver, may give some 

 idea of this member in the primitive Cetacea. 



As pointed out long ago by Hunter, there are numerous points in 

 the structure of the visceral organs of the Cetacea far more resembling 

 those of the Ungulata than the Carnivora. These are the complex 

 stomach, simple liver, respiratory organs, and especially the reproduc- 

 tive organs and structures relating to the development of the young. 

 I can not help thinking that some insight has been shown in the com- 

 mon names attached to one of the most familiar of Cetaceans by 

 those whose opportunities of knowing its nature have been greatest 

 " sea-hog," " sea-pig," or " herring-hog," of our fishermen, Meerschwein 

 of the Germans, corrupted into the French " marsouin," and also 

 "porcpoisson," shortened into "porpoise." A difficulty that might be 

 suggested in the derivation of the Cetacea from the Ungulata, arising 

 from the latter being at the present day mainly vegetable-feeders, is 

 not great, as the primitive ungulates were probably omnivorous, as 

 their least modified descendants, the pigs, are still ; and the aquatic 

 branch might easily have gradually become more and more piscivorous, 

 as we know, from the structure of their bones and teeth, the purely 

 terrestrial members have become by degrees more exclusively grami- 

 nivorous. 



One other consideration may remove some of the difficulties that 

 may arise in contemplating the transition of land mammals into whales. 

 The Gangetic dolphin (Platanista) and the somewhat related Inia of 

 South America, which retain several rather generalized mammalian 

 characters, and are related to some of the earliest known European 

 Miocene forms, are both to the present day exclusively fluviatile, being 

 found in the rivers they inhabit almost up to their very sources, more 

 than a thousand miles from the sea. May this not point to the fresh- 

 water origin of the whole group, and thus account for their otherwise 

 inexplicable absence from the Cretaceous seas ? 



