A series of experiments has been carried out which show that the fecundity (the number of eggs laid) and the longevity of E. cautella Wlk. and E. Clutella Hb. are about halved if they are deprived of drinking-water, but that E. kühniella Z. is only slightly affected by it. It was also found that sugar-feeding further increased tho longevity of E. kühniella and E. cautella, but did not increase the fecundity any more than water. When E. cautella was fed on albumen and water it lived no longer and laid no more eggs than when fed on water alone. A more detailed summary of the results of these experiments is given on p. 350. Chemical tests showed that the enzyme invertase is present in the gut of both E. cautella and E. kühniella. A summary of the literature concerning these questions in insects in general and more particularly in the Lepidoptera shows that, whereas a sugar diet suffices to maintain life, most adult insects require proteins of some kind for the normal development of their genital products, and in many insects oviposition is entirely conditional upon the taking of such food. The adult Lepidoptera Heteroneura have, as far as is known, completely lost the need for nitrogenous foodstuffs owing to a series of modifications by which their requirements have come to be met by the food stored in tho fat-body. Table L. shows the probable evolutionary trends which have finally brought about such complete liberation from the need of food that, in the final stage, the mouth-parts are reduced and no food at all is taken. The various characters involved in these trends do not appear to have been modified simultaneously (e. g., enzymes may persist after the need for them has been lost).