xv SPECULATIONS AS TO ORIGIN 231 



and more piscivorous, as we know from the structure of their 

 bones and teeth, the purely terrestrial members have become 

 by degrees more exclusively graminivorous. 



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 generalised mammalian characters, and are related 

 to some of the earliest known European Miocene dolphins, 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 freshwater origin of the whole group, and thus account for 

 their otherwise inexplicable absence from the Cretaceous seas ? 



We may conclude by picturing to ourselves some primitive 

 generalised, marsh-haunting animals with scanty covering of 

 hair like the modern hippopotamus, but with broad, swimming 

 tails and short limbs, omnivorous in their mode of feeding, 

 probably combining water-plants with mussels, worms, and 

 freshwater crustaceans, gradually becoming more and more 

 adapted to fill the void place ready for them on the aquatic 

 side of the borderland on which they dwelt, and so by degrees 

 being modified into dolphin-like creatures inhabiting lakes and 

 rivers, and ultimately finding their way into the ocean. Here 

 the disappearance of the huge Enaliosaurians, the Ichthyosauri 

 and Plesiosauri, which formerly played the part the Cetacea 

 do now, had left them ample scope. Favoured by various 

 conditions of temperature and climate, wealth of food supply, 

 almost complete immunity from deadly enemies, and illimitable 

 expanses in which to roam, they have undergone the various 

 modifications to which the Cetacean type has now arrived, and 

 gradually attained that colossal magnitude which we have seen 

 was not always an attribute of the animals of this group. 



Please to recollect, however, that this is a mere speculation, 

 which may or may not be confirmed by subsequent palaeonto- 

 logical discovery. Such speculations are, I trust, not without 

 their use and interest, especially when it is distinctly under- 

 stood that they are offered only as speculations and not as 

 demonstrated facts. 



