INSTINCTS APPARENTLY DETRIMENTAL TO THE SPECIES. 283 



still a vast multitude, plunges into the Atlantic Ocean on 

 the first calm day and perishes with its front still pointing 

 westward. No faint heart lingers on the way, and no sur- 

 vivor returns to the mountains. Mr. R. Collett, a Norwegian 

 naturalist, writes that in November, 1868 (quoted by Fille- 

 burg, infra) y a ship sailed for fifteen hours through a swarm of 

 Lemmings, which extended as far over the Trondhjemsfiord as 

 the eye could reach."* 



Such, according to i\Ir. Crotch, are the facts, and the follow- 

 ing are the hypotheses which have been propounded to ex- 

 plain them. Mr. Wallace suggests! that natural selection has 

 played an important part in causing migration, by giving an 

 advantage to those animals which enlarge their breeding area 

 by travel. To this view, as applied to the lemming, Mr. 

 Crotch objects that the animal, " it is true, always breeds 

 during migration ; but if none return or survive, it is difficult 

 to say what becomes of the fittest." His own theory is a 

 remarkable one. " There is," he says, " a solution of this 

 difficulty, involving a subject of the deepest interest, and 

 which led me to spend two years in the Canaries and adjacent 

 islands. I allude to the island or continent of Atlantis. , . 

 It is evident that land did exist in the North Atlantic Ocean 

 at no very distant date. . . . Is it not then conceivable, 

 and even probable, that when a great part of Europe was 

 submerged and dry land connected Norway with Greenland, 

 the lemmings acquired the habit of migrating westward for 

 the same reasons which govern more familiar migrations ? 

 . . . It appears to me quite as likely that the impetus 

 of migration towards this continent should be retained as 

 that a dog should turn round before lying down on a rug, 

 merely because his ancestors found it necessary thus to 

 hoUow out a couch in the long grass." 



In a later paperj he combats by the aid of charts the 

 popular theory " that these migrations follow the natural 

 declivities of the country," and then proceeds to add, " It is 

 very remarkable that the average depth from Norway to Ice- 

 land does not exceed 250 fathoms, with the exception of a 

 deep and narrow channel of 682 fathoms at 14° W. This 

 probably represented the old Gulf Stream ; and if this were 

 so, the lemmings did wisely to migrate westwards in search 



* Linn. Soc. Jour., toL xiii, p. 30, et seq. f I^ature, voL x, p. 459. 

 X Lmn. Soc. Jour., voL xiii, p. 157, et ,seq. 



