120 Prof. M'lntosh on the 



themselves to every vicissitude of climate. Nor do their 

 layers of fat seem to present notable differences in the several 

 regions. As they are piscivorous, their food is obtained 

 without difficulty in every ocean and river. The killer ( Orca) 

 is likewise cosmopolitan, its chief food consisting of seals and 

 porpoises. Ghbicepholus mclas has also a wide range — from 

 the northern seas to the Cape and New Zealand — and Tarsiops 

 is nearly as extensively distributed. 



On the other hand, most of the species of Sotalia are 

 fluviatile, occurring in China and with Into and Pontoporia 

 in the Amazons and other rivers of South America, whilst 

 one species (a vegetable feeder) frequents the Cameroon 

 River. 



With a distribution so complex, in an element which offers 

 no obstacle (except temperature, safe surroundings, and food) 

 to a cosmopolitan range for every species of marine cetacean, 

 the question as to the explanation of these diversities presents 

 itself. Why does Beluga not frequent European seas, or 

 Btrardius of New Zealand stretch far northwards into the 

 Pacific? Beyond the answer that each finds in its special 

 area suitable environment and the food best fitted for it, no 

 answer is at present available. Hereditary tendencies, pecu- 

 liarities of stiucture, and habit are, perhaps, responsible for 

 the pertinacity with which the anomalous dolphins, like 

 Platamsta, cling to fresh water, though it is true one genus 

 (JSotaHa) is found equally in the Amazon and the sea. Nor 

 does the distribution of the whales throw much light on their 

 origin. So far as facts warrant, it would appear that the 

 toothed whales are the primary forms from which those with 

 whalebone have been evolved, but whether from a marine or 

 a freshwater form cannot yet be answered with certainty, 

 though the number of oceanic species shows that the sea at 

 least proved a congenial area. The enormous lapse of time 

 necessary for the development of the various groups further 

 indicates that the ocean-basins are of great antiquity, though 

 they may not always have had the same conformation. 



The distribution of certain birds (which pass most of their 

 time at sea), such as penguins, auks, grebes, divers, and 

 guillemots — all, with the exception of the first, possessing the 

 power of flight, — is limited to the colder areas ; yet there is 

 HO serious impediment to their ranging over a much larger 

 field except the difficulty of a secure breeding-place and the 

 question of temperature. Food is everywhere abundant. In 

 all probability it is the safety and convenience of their 

 " rookeries" which keep the penguins to the southern seas. ■ 



