INTRA-SELECTION OR SELECTION AMONG TISSUES 251 



admit that the insight we have so far gained into the causes of these 

 adaptations does not make it much easier to answer the question. 

 Histonal selection is a purely local process of adaptation to the con- 

 ditions of stimuli prevailing at the moment, and no one will be likely 

 to suppose that the distorted position of the spongiosa of a badly 

 healed fracture could reappear in the straight bone of a descendant ; 

 this would be quite contrary to the principle, for the crooked lamellae 

 would in that case no longer be the best adapted. Even the question 

 whether the strengthening of a muscle through use can he transmitted 

 cannot be answered in the light of the knowledge we have hitherto 

 gained. The ' trophic effect of the functional stimulus ' is brought 

 into activity through entirely local influences, through which only 

 the parts most strongly affected by the stimulus can be caused to vary. 

 Thus the problem remains unaltered, How can purely local changes, 

 not based in the germ, but called forth by the chances of life, be 

 transmitted to descendants ? 



If all species, even in the highest groups, reproduced by dividing 

 into two, we might imagine that a direct transmission of the changes 

 acquired in the course of the individual life through use or disuse 

 took place, though this would presuppose a much more complicated 

 mechanism than is apparent at first sight. But it is well known that 

 multiplication by fission is for the most part restricted to simple 

 organisms, and that the great majority of modern plants and animals 

 reproduce by means of germ-cells, which develop within the organism 

 in regions often very remote from the parts, the results of the exercise 

 of which are said to be transmitted. Moreover, the germ-cells are of 

 very simple structure, at least as far as our eyes can discern ; for we 

 see in a germ-cell neither muscles nor bones nor ligaments, glands nor 

 nerves, but only a cell-body consisting of that semifluid living matter 

 to which the general name of protoplasm has been given, and of 

 a nucleus, in regard to which we cannot say that it difiers in any 

 essential or definite way from the nucleus of any other cell. How 

 then could the changes which take place in a muscle through exercise, 

 or in the degeneration of a joint in consequence of disuse, communicate 

 themselves to a germ-cell lying inside the body, and do so in such 

 a fashion that this germ-cell is able, when it grows into a new 

 organism, to produce of itself, in the relevant muscle and joint, 

 a change the same as that which had arisen in the parent through 

 use and disuse? That is the question which forced itself upon me 

 very early, and in following it up I have been led to an absolute 

 denial of the transmission of this kind of ' acquired characters.' 



In order to explain how I reached this result, and what it is 



