578 FROM NORTH POLE TO EQUATOR. 



likely enough, but the captain of our boat added, that occasionally the 

 crocodile falls asleep, when the jaws suddenly fall, and the zic-zac is shut 

 up in the mouth, when it immediately prods the crocodile with its horny 

 spurs, as if refreshing the memory of his reptilian majesty, who opens his 

 jaws and sets his favourite leech-catcher at liberty " (Leith Adams). 



MIGRATIONS OF MAMMALS. 



Note 56, p. 237. Rats, 



The brown rat (Mus decumanus) is much stronger than the black rat 

 (Mus rattus), and gains an easy victory. The rivalry between the two 

 species is one of the examples Darwin gives of his generalization that the 

 struggle for existence is most severe between allied forms, and there seems 

 no doubt that the brown rat has often ousted and will even devour the 

 black rat. The latter is now rare in Britain. It should be noted, how- 

 ever, (1) that the two species are said sometimes to live together on board 

 ship, (2) that cases have been recorded where the black rat returned and 

 defeated its conquerors, and (3) that the black rat keeps more about houses, 

 stables, and barns, is therefore more readily exterminated by man, whose 

 efforts were doubtless increased when a second species appeared on the 

 scene. The case is of some importance in connection with the generaliza- 

 tion referred to above. 



Note 57, p. 240. Migrations of Reindeer. 



Of the reindeer in Spitzbergen, Nordenskiold writes: "During the 

 summer it betakes itself to the grassy plains in the ice-free valleys of the 

 island ; in the late autumn it withdraws according to the walrus-hunter's 

 statements to the sea-coast, in order to eat the seaweed that is thrown 

 up on the beach. In winter it goes back to the lichen-clad mountain 

 heights in the interior of the country, where it appears to thrive exceed- 

 ingly well, though the cold during winter must be excessively severe ; for 

 when the reindeer in spring return to the coast they are still very fat, but 

 some weeks afterwards, when the snow has frozen on the surface, and a 

 crust of ice makes it difficult for them to get at the mountain sides, they 

 become so poor as to be scarcely eatable. In summer, however, they 

 speedily eat themselves back into condition, and in autumn they are so fat 

 that they would certainly take prizes at an exhibition of fat cattle." 



"Wrangel describes migrations of thousands of reindeer in Eastern 

 Siberia moving from the mountains to the forests, where they winter. He 

 mentions his guide's assertion that each body is led by a female of large 

 size. 



Perhaps we may take the liberty of quoting, with a tribute of admira- 

 tion, Mr. F. Marion Crawford's eloquent description of a wild rush of 

 reindeer from the inland country to the shore. We confess to incredulity 

 in regard to the reindeer's longing to drink of the Polar Sea, but the 

 splendid vividness of the description may excuse some slight inaccuracy. 



