96 



THE AMERICAN NATURALIST [Vol. XL V 



the body of the offspring. This conception has taken 

 various forms, commencing with Darwin's hypothesis of 

 * ' pangenesis. ' ' The same general view has recently been 

 restated in chemical terms, and in a manner which is 

 perhaps far less shocking to our common sense. 



The other alternative is that of a "parallel induction" 

 or ' 1 simultaneous modification of the germ-plasm," 

 through the direct action of the modifying agent. This 

 explanation, as we all know, has been freely used by 

 Weismann and others to account for a considerable range 

 of phenomena, notably the persistence of temperature 

 effects in a second generation of butterflies. The phrase 

 has indeed become so familiar through long repetition 

 that few of us stop to consider just what it implies. 

 ."Parallel modification of the germ-plasm!" How can 

 the unformed material of the germ cells be modified in the 

 same manner as certain groups of somatic cells — say in a 

 butterfly's wing — even by an all-pervading influence like 

 temperature? This is obviously not what is intended. 

 What we mean, concretely stated, is this: the germinal 

 matter is so affected by the temperature that, after some 

 hundreds or thousands of cell generations, certain of the 

 resulting cells will show peculiarities in their pigment- 

 producing powers of the same nature as those which 

 arose directly in the somatic cells of the parent. And a 

 most curious feature of this coincidence is that these 

 modified cells are situated in precisely the same parts of 

 the body in the one case as in the other. 7 



Thus do these very simple explanations have a way of 

 losing their simplicity when examined critically. In the 

 present instance, the hypothesis stated may, for all we 

 know, be the one that most nearly represents the truth. 

 But it should be stated frankly, in all its complexity, and 

 not palmed off upon us as a readily intelligible hypoth- 

 esis, which relieves us of the necessity of adopting an 

 "inconceivable" one such as that of pangenesis. 



the solution thus offered is almost wholly a formal one. g 



