THE CEAB-EATING SEAL. 33 



and Leptonychotes, since they are by far the most abundant of the five seals now known 

 to occur within the Antarctic circle. 



Ommatophoca is still a rarity ; Stenorhinchus, though less rare, is very sparsely 

 distributed, and Macrorhinus can only be considered a very occasional visitor, thus 

 leaving Leptonychotes and Lobodon as the two seals that occur in great numbers to share 

 the field between them. This they have done by differentiating both in habit of life 

 and in diet, Lobodon living mainly upon crustaceans, and Leptonychotes almost wholly 

 upon fish. 



It is noticeable that the two penguins which share the same area have differen- 

 tiated in a somewhat similar manner, the Emperor living almost entirely upon fish, 

 and the Adelie Penguin almost entirely upon crustaceans. If we press the similarity 

 even further, we shall see that Weddell's Seal and the Emperor Penguin have 

 similarities which are distinct from the similarities that exist between the Crab-eater 

 and the Adelie Penguin. 



The first two have the following points in common, namely, a littoral distribu- 

 tion, a fish diet, and residental non-migratory habit, remaining as far south the whole 

 year round as open water will allow ; whereas the other two, Lobodon and Pygoscelis 

 adelice, have in common a more pelagic habit, a crustacean diet, and a distribution 

 definitely migratory in the case of the penguin, and although not so definitely 

 migratory in the case of the seal, yet checked from coming so far south as Weddell's 

 Seal in winter by a strong tendency to keep in touch with pelagic ice. By this 

 differentiation, the interests of Lobodon and Leptonychotes are saved from clashing, as 

 are also the interests of the two penguins ; and the advantage in each case rests appa- 

 rently with the non-migratory and more southern species. For one thing, at any rate, 

 both Weddell's Seal and the Emperor Penguin are very much more free from the 

 attack of beasts and birds of prey than are either Lobodon or Pygoscelis adelice. 



The attentions of Orca gladiator are confined almost wholly to Lobodon, and those 

 of Megalestris maccormicki almost wholly to Pygoscelis adelice. Neither Orca nor 

 Megalestris can be considered to play any great part in the life history of Weddell's 

 Seal or of the Emperor Penguin. In this respect, no doubt, these two animals have 

 made a great advance by accommodating themselves to the winter conditions which 

 prevail in the highest latitudes where water, and therefore food, can by any means be 

 obtained. 



There is, at present, but slender basis for saying that Lobodon is a migratory seal 

 in any sense, but it was noticeable that so long as open water was within a mile or two 

 of our winter quarters, we were occasionally visited by this seal, whereas it entirely 

 disappeared and was not once seen when and so long as five or ten miles of solid ice 

 separated us from open water ; although Leptonychotes, as I have already shown, was 

 almost as abundant as before. 



In the month of February, for example, during our first year in McMurdo 

 Sound, we saw three Crab-eaters on the 25th, and these remained with us till the 



VOL. II. D 



