LECTURE XXXI 

 THE INFLUENCES OF ENVIRONMENT 



Different modes and grades of selection— Changes due to the influences of environ- 

 ment— Superfluitj-^ and lack of food— The horses and cattle of the Falkland Islands- 

 Angora animals — Protection against cold in Arctic and ma^'ine mammals — Plant-galls 

 — Nageli's Hieracium experiments — Experiments v^r'ith Folyovimatus iMceas — Artificially- 

 produced Fanessrt-aberrations— Vochting's experiments on the influence of light in the 

 production of flower-forms — Heliotropism and other tropisms— Primary and secondary 

 reactions of organisms — Herbst's 'lithium larvte ' — Schmankewitsch's experiments 

 with Artemia — Poulton's caterpillars with f^icultative colour adaptation — Colour-change 

 in fishes, chamaeleon, &c. — Actual scope of those infiuences which directly produce 

 organic changes. 



Thkough a long series of lectures we have devoted our attention to 

 those phenomena which bear some relation to the processes of selection ; 

 we have attempted to gain clearness in regard to the modes and stages 

 of these, and we reached the result that all variations which have 

 taken place in organisms since the first appearance of living matter 

 are directed by processes of selection, that is, their direction and 

 duration are determined by these processes, although they may have 

 their roots in external influences. But it is not to be supposed that 

 this guidance is due solely to that one kind of selection which, with 

 Darwin and Wallace, we designate 'natural selection'; on the contrary, 

 we must regard this as only one of the different modes of the processes 

 of selection, necessarily occurring between all living units which are 

 equivalent to one another, and which, therefore, must maintain a con- 

 tinual struggle with one another for space and food. If the expression 

 ' natural selection ' were not already so hrmly fixed in its meaning, 

 I should propose that it should be employed in the most general sense 

 for all the processes of selection collectively, but we must keep to its 

 original meaning and use it only for personal selection. 



We have seen that processes of selection take place even between 

 the elements of the germ-plasm in all organisms which possess a germ- 

 plasm as distinguished from the mass of the body, and that through 

 these processes there arise those hereditary individual variations 

 which, under some circumstances, form the basis of transformations 

 in the species. 



Obviously this may come about in a twofold manner: firstly, 



