102 THE EVOLUTION THEORY 



functioning more strongly changes the composition of the blood, by 

 withd^a^Ying from it in a greater degree the specific substances which 

 the organ in question— a muscle, for instance — requires for its activity. 

 All parts of the animal are thereby affected and modified, but especially 

 those smallest vital units or ' fistellse ' (corresponding to biophors) which 

 preside over digestion, and of which there are several sorts. Among 

 them those work most arduously which have to produce the specific 

 substances which serve for the nutrition of the muscles with increased 

 function, because these are needed in larger quantities. This kind of 

 digestive ' fistella ' therefore multiplies, while other kinds, whose 

 products are not required and therefore not used up, cease to be so 

 active, diminish in number, and in course of time disappear. In this 

 way the composition of the blood is altered, and with it to a greater 

 or less degree all the characters of the whole organism. Of course 

 the reproductive cells are also under the influence of this change in 

 the composition of the blood, because the different nutritive substances 

 are accumulated within them in an altered proportion corresponding to 

 the changed composition of the blood, the nutritive substances for the 

 muscles with increased function being contained in it in a larger 

 quantity, and thus the greater development of the muscle will repeat 

 itself in the progeny, that is to say, tlte acquired character is trans- 

 Tiiitted. 



It is obvious that this is precisely the same line of argument as 

 that used in reference to the orio-in of the worker and soldier ants. 

 The different kinds of * digestive fistellae ' correspond to the different 

 food-carrying workers, and the blood to the assumed storehouse from 

 which soldiers and workers select the food suitable for their respective 

 needs, while the sex-cells in the one case, the sexual animals in the 

 other, partake of all kinds exactly in the proportion in Avhich they are 

 stored, and thus the organ which functions most vigorously must be 

 stronger in the offspring. 



How the minute quantity of nutritive material contained in the 

 ovum, still less in the sperm, is to effect the strengthening of the parti- 

 cular muscles in the descendants is not stated ; moreover, such minimal 

 quantities of food must soon be exhausted, and cannot possibly 

 increase. It would seem as if the muscles could not even begin by 

 being stronger, much less that they should remain so, if they were not 

 exercised equally vigorously by the descendants. If the specific 

 nutritive stuffs were ' fistellse,' that is to say, were living units capable 

 of multiplication, one could understand it. But there can, of course, 

 be no possibility of a production of living units through digestion ; 

 that can only give rise to digested substances. Or if the alteration in the 



