ASPECTS OF MODERN BIOLOGY 545 



man. The competition between allied species is thus often indirect, 

 one destroying another by conveying to it some disease. 



The flax is visited by various bees, which I have studied and 

 recorded; these carry the pollen from flower to flower, and thus aid in 

 pollination. Whether the necessary bees are always present, is not yet 

 known; but their presence in numbers must be a favorable factor, and 

 thus an important element in the living environment. 



In the case of the snail, although it is so common, we know little 

 or nothing about its natural enemies. 



The more we study living creatures the more we become impressed 

 by the complicated conditions necessary for the preservation of the 

 higher forms, and the possibilities of local or complete extermination. 

 As we determine these more accurately, we feel able to return to the 

 fossils, and from them restore the past in much more detail than at 

 first seemed possible. If a snail or a slug crossed from Asia to America 

 we presume that it not only found continuous, or nearly continuous, 

 land, but also that it did not traverse any desert. The path of migra- 

 tion of the blue flax was not, it is virtually certain, across a lowland 

 region or swamp. Making all allowances for what are called acci- 

 dental means of transportation, it ought to be possible to infer some- 

 thing about the pathway of a considerable number of species. 



In all of these researches, success and failure are inextricably 

 mixed, at least as regards the details. In no case can we gather all 

 the pertinent facts; our knowledge of even the commonest species is 

 very deficient. Yet, when all is taken together, we find ourselves like 

 the man who said he lost on every job, but was able to make money 

 because of the multitude of them. The number of known species, 

 living and extinct, is enormous, and the data we have gathered, when 

 suitably sorted and arrayed, will point to many definite conclusions. 

 More especially is there reason to hope for good results to be derived 

 from studies which past investigations have merely suggested and shown 

 to be possible. 



As a matter of history, as food for the imagination, it is interesting 

 enough to watch and take part in the reconstruction of the past, espe- 

 cially when we are able to do this with a reasonable degree of com- 

 pleteness, as at Florissant in Colorado, or (Eningen in Germany. Much 

 more, however, may come of these investigations. The problems of 

 evolution, the intricate questions of heredity and variation, may be 

 answered in part by such means as I have described. 



The experimentalists, represented by Bateson, De Vries, Tower, 

 MacDougal, Davenport and many others, have ascertained that what 

 appear to be new species or races may arise suddenly by a process 

 termed mutation. It even appears that in certain cases this process 

 may be brought about by artificial means, such as differences of humid- 



VOL. LXXIII. — 35. 



