Ci. the Proportion of Skeletal Tissues in Insects

THE proportion of the skeleton to the weight of the whole insect might be needed for many purposes. My own reason for enquiring is that I have subjected insects to controlled atmospheric conditions, determiing the loss of weight and the proportion of water in the insect before and after exposure. But when it has been demonstrated that under certain conditions the insect loses a particular amount of water and of dry material, it is not known how much of the remaining dry material is living matter on which the insect could perhaps call for energy, and how much of it is "dead" skeleton. It is the purpose of this note to discuss methods of estimating the weight of skeletal tissues in insects. It is known that a considerable portion of the hard exo-skeleton of insects consists of substances other than chitin. Campbell [1929], for instance, has shown that in Periplaneta and several other insects the chitin makes up 30 to 40 % of the skeleton'. It is not known what the other materials are, though it is generally held that they consist (in part at least) of scleroproteins. For the moment it would suffice if an empirical figure for "skeleton" could be obtained. The proportion of chitin to skeleton differs in different parts of the same insect, and doubtless also in different species of insects. It is therefore not possible to estimate the chitin and deduce the total weight of skeleton from it. EXPERIMENTS WITH MEAL-WORMS.