768 THE POPULAR SCIENCE MONTHLY. 



cumulates ; so that two, three, or more generations must be exposed 

 to new conditions before any effect is visible," implies that during 

 these generations there is going on some change of constitution con- 

 sequent on the changed proportions and relations of the functions. I 

 will not dwell on the implication, which seems tolerably clear, that 

 this change must consist of such modifications of organs as adapt them 

 to their changed functions ; and that if the influence of changed con- 

 ditions "accumulates," it must be through the inheritance of such 

 modifications. Nor will I press the question — What is the nature of 

 the effect registered in the reproductive elements, and which is subse- 

 quently manifested by variations ? — Is it an effect entirely irrelevant 

 to the new requirements of the variety ? — Or is it an effect which 

 makes the variety less fit for the new requirements ? — Or is it an effect 

 which makes it more fit for the new requirements ? But not pressing 

 these questions, it suffices to point out the necessary implication that 

 changed functions of organs do, in some way or other, register them- 

 selves in changed proclivities of the reproductive elements. In face 

 of these facts it cannot be denied that the modified action of a part 

 produces an inheritable effect — be the nature of that effect what 

 it may. 



The second of the remarks above adverted to as made by Mr. Dar- 

 win, is contained in his sections dealing with correlated variations. In 

 the Origin of Species, p. 114, he says : 



" The whole organization is so tied together during its growth and develop- 

 ment, that when slight variations in any one part occur, and are accumulated 

 through natural selection, other parts become modified." 



And a parallel statement contained in Animals and Plants under Do- 

 mestication, vol. ii, p. 320, runs thus : 



" Correlated variation is an important subject for us; for when one part is 

 modified through continued selection, either by man or under nature, other parts 

 of the organization will be unavoidably modified. From this correlation it appar- 

 ently follows that, with our domesticated animals and plants, varieties rarely or 

 never differ from each other by some single character alone." 



By what process does a changed part modify other parts? By. 

 modifying their functions in some way or degree, seems the necessary 

 answer. It is indeed, imaginable, that where the part changed is some 

 dermal appendage which, becoming larger, has abstracted more of the 

 needful material from the general stock, the effect may consist simply 

 in diminishing the amount of this material available for other dermal 

 appendages, leading to diminution of some or all of them, and may 

 fail to affect in appreciable ways the rest of the organism : save per- 

 haps the blood-vessels near the enlarged appendage. But where the 

 part is an active one — a limb, or viscus, or any organ which constantly 

 demands blood, produces waste matter, secretes, or absorbs — then all 

 the other active organs become implicated in the change. The functions 



