How the minute quantity of nutritive material contained in the ovum, still less in the sperm, is to effect the strengthening of the particular 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 'fistellæ,' 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 composition of the blood produced in the determinant system of the germ-plasm just those variations requisite to bring about a strengthening 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 of 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 substances 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.