THE CRAB-EATING SEAL. 38 
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 Adélie 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 Adélie 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 
adelie, 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 adelic. 
The attentions of Orca gladiator are confined almost wholly to Lobodon, and those 
of Megalestris maccormicki almost wholly to Pygoscelis adeliw. 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. Il. D 
