796 POPULAR SCIENCE MONTHLY. 



speculation which geology affords, and it has been gravely suggested 

 that the migration of the lemmings and their death in the waters 

 of the ocean may be due to their efforts to reach the lost Atlantis, 

 where their ancestors dwelt during the Miocene period, although 

 this opinion has no better basis than the belief of Olaus Magnus that 

 they rain down from the sky, where they are engendered from the 

 decomposing exhalations from the clouds impregnated by the semen 

 of rats. 



It is easy to understand how birds near the northern limit of 

 their range invade the territory of those whose home is a little 

 farther south, and compete with them for food as this becomes 

 scarce- with the approach of winter, and how this movement spreads 

 until all the members of the species are involved, although many of 

 them might have been able to subsist some time longer in their 

 breeding ground if they had been undisturbed. 



We have seen that this has commended itself to northern natural- 

 ists as a sufficient reason for the acquisition of the migratory habit, 

 and the fondness for their birthplace which is so strongly marked in 

 birds has been thought enough to draw them back; but love of home 

 is itself a result of natural selection, and the necessity for finding safe 

 places for the eggs and young is enough to account for the migration 

 without the aid of geological changes. 



"While we know little as to the means by which birds find their 

 way over land and water, we know that, as a matter of fact, they are 

 able to do so; and we also know that the instinct which leads them 

 to seek safe places for their nests is so firmly implanted in their 

 nature that centuries of domestication weaken it but little, for it is 

 still almost as strong in the Guinea fowl and the turkey and the 

 hen as it is in wild birds. As birds of powerful flight have a range 

 of choice almost as wide as the earth itself, it is not surprising that 

 the continual destruction of those born in the least safe nests has at 

 last resulted in the survival of the ones which make their nests thou- 

 sands of miles away from their natural or ancestral home. 



While most writers have thought migration had its origin in an 

 annual journey which, while short, was definitely fixed for all the 

 members of the species, and while they have felt forced to call in the 

 aid of geology to account for the gradual separation of the two 

 termini and the lengthening of the journey, the hypothesis of geo- 

 logical change seems gratuitous and unnecessary, since the known 

 habits and instincts and needs of the birds are in themselves a suf- 

 ficient explanation of all the broader and more general character- 

 istics of migration. It seems much more simple, and more con- 

 sistent with our knowledge of the past history of living things in 

 general, to believe it had its origin in an intense but geographically 



