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 part. At this particular spot, then, the chitin will be specially thick. This clearly implies that each particular part of the skin has its specific nutritive substances, necessitated by the nerves which traverse it! Thus there must be as many nerve-nutritive substances as there are skin-nerves, specific chemical combinations for every part of the body which is capable of heritable variation. This is so extraordinarily improbable that I need say nothing more about it. If the Lamarckian principle requires this kind of hypothesis to bolster it up, it is undoubtedly doomed. If we disregard altogether the positive aspect of Zehnder's hypothesis, and assume that the skin-nerves are really stimulated through the chitin by every strain and pressure to which a spot of skin is exposed, and that they cause a correspondingly greater secretion of chitin, which would then, according to the Lamarckian principle, be hereditary, does this harmonize with what actually occurs in the development of the skeleton as we know it in the case of Insects and Crustaceans? Not at all! Can we suppose that the carapace of a crab or the enormously hard wing-covers of a water-beetle are exposed to a continual pounding and pressing and pushing? Exactly the contrary is the case. Every assailant takes care not to grasp the animal where it is so well protected, and seeks out the most vulnerable parts for its attacks. It may be answered that, while this is certainly the case now, the animals were badly protected when the ancestral forms were evolving. But that they could not have become hard by dint of being frequently bitten or otherwise wounded should be obvious from the fact that the whole of the wing-covers and the whole of the carapace is uniformly covered with thick chitin, while each wound would only stimulate particular spots; and we should also have to admit that, since these parts of the skin which are now so well protected are no longer seized and stimulated, they would long ago have become thin again, according to the principle of the degeneration of parts no longer used, or, in this case, no longer stimulated.