784 POPULAR SCIENCE MONTHLY. 



we had taken our last drive, *my companion gave our driver a small 

 fee, saying that it was because he was such a good botanist, for he 

 really had been able to tell us the popular names of many plants. 

 He laughed, and as he seemed so much pleased, I said, " James, I 

 suppose you know what botanist means? " " Yes," he answered, 

 " I 'spose it's some kind of a good boy." 



MIGBATION. 



- 



By W. K. BROOKS, LL.D., 



PROFESSOR OF ZOOLOGY IN THE JOHNS HOPKINS UNIVERSITY. 



IT is easy to understand how natural selection may modify organ- 

 isms for the good of the species, even at the expense of the in- 

 dividuals which, in each generation, make up the species; but it is 

 difficult to understand how this can be brought about by nurture, 

 for, so far as the direct action of the conditions of life is concerned, 

 the species is identical with the sum of the individuals which now 

 exist. No illustration of the law that the adaptations of living Nature 

 are for the good of the species, and that when this comes into con- 

 flict with the welfare of the individuals, these are sacrificed, is more 

 simple or more easy to understand than that afforded by some of the 

 phenomena of migration. 



The young salmon which is born in a mountain stream is soon 

 impelled, by something in its nature, to journey downward, even 

 for many hundred miles, until it reaches the unknown ocean, where 

 it would discover, if it had faculties for anything so subjective as dis- 

 covery, that, while it was born in a little brook, it was made for life 

 in the great ocean. It has brought from its mountain home a 

 natural aptitude for eluding all the strange enemies and for avoid- 

 ing all the novel dangers which it meets in this new world, and 

 it leads an active, predatory life, fiercely pursuing and destroy- 

 ing its natural but hitherto unknown prey; for growing rapidly, 

 and quickly acquiring all the characteristics of the adult salmon, 

 and storing up the intense nervous energy and the muscular 

 strength which will be needed for forcing its way up the rapids 

 in the mountain torrents, for leaping waterfalls, and fighting for 

 its passage, where it long ago darted down with the current. As 

 sexual maturity approaches, some stimulus, which has its origin in 

 the developing reproductive organs, impels it to leave the ocean and, 

 entering the mouth of a river, to journey upward, often a thousand 

 miles or more, to its sources in the mountains. 



At this time the king of fishes, as it is well called, is in physical 

 perfection, with few rivals in beauty or strength or fierce energy, or 



