TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 103 



composition of the blood produced in the determinant system of the 

 germ-plasm just those variations requisite to bring about a strength- 

 ening of the muscular system, it would remain to be shown how this 

 could happen, for the gist of the problem lies in this. For muscles 

 do not lie in the germ-plasm as miniature models of the subsequent 

 muscular system, and even if they did, would not all the muscles, and 

 not merely those which were no longer exercised, decrease hereditarily 

 when a particular group, like the muscles of the ear in man, 

 degenerates? Zehnder replies to this with the hypothesis that the 

 muscles are not all chemically alike, but that each possesses a 

 particular chemical formula, though they may all be very similar, and 

 that, therefore, the nutritive materials required by each must be 

 slightly different. In that case there would require to be, in the ovum 

 and sperm of man, in order that functional modifications might be 

 transmitted, as many special nutritive substances as there are muscles, 

 and, in addition to these, innumerable hosts of other kinds ©f specific 

 nutritive substances for all the other parts of the body, since all of 

 them can be strengthened by exercise and weakened by disuse. And 

 even if we suppose that all these millions of specific nutritive sub- 

 stances are accommodated within the germ-cells, as Zehnder 's theory 

 requires, they could not perform what Zehnder ascribes to them, for, 

 as we have already said, they cannot multiply in the manner of living- 

 units, and so control the growing organism. The different specific 

 nutritive materials contained in the blood are just as powerless to 

 perform the task ascribed to them by Zehnder as the specific kinds of 

 food in the hypothetical storehouse of the ants are to give rise to the 

 different persons of the ant-colony. 



Zehnder also attempts to overthrow the arguments against the 

 Lamarckian principle which I based on the skeleton of Arthropods. 



It does not seem to him probable that the chitinous coat of mail 

 can be an absolutely dead structure, and he supposes that very delicate 

 nerve-fibrils penetrate into all its most minute parts, and so are 

 stimulated by ' every pressure and every strain ' exerted on the 

 chitinous skeleton. They ' work ' when they are stimulated, and in 

 doing so they use up ' their specific food-stuffs.' At places which are 

 frequently stimulated the corresponding nerves develop more than 

 elsewhere. The necessary specific food-stuffs for these particular 

 nerves therefore increase proportionately within the body, and 

 also in the reproductive cells. Accordingly, in the germ-cells there 

 is an increase of the aforesaid nervous substances, which in the 

 offspring become associated with the relevant part of the chitinous 

 covering, and induce in development the secretion of chitin at this 



