ON THE COMPARATIVE OECOLOGY OF THE BLOOD-SUCKING DIPTERA. 1. THE DOUBLE ROLE OF THE CROP IN THE WATER-ECONOMY OF MOSQUITOS

The rapid injection of small doses not higher than half the body weight of distilled water into the body cavity does not do the insect any harm. The injection of more massive doses not exceeding, however, the quantity of water which the insect could drink is often lethal ... apparently in those cases when the haemolymph concentration is already quite low to begin with. Liquid injected parenterally or more properly speaking, in any other way than via the crop is expended by the mosquito at a very extravagant rate the whole of its excess liquid is rapidly excreted by way of the Malpighi canals, and only slight use made of it to cover expenditures in the normal water-economy of the insect. Thus the crop, with its water-impermeable wall and the very slow transfer of its contents to the mid-intestine, is an adaptation which in the first place guarantees the economical use of imbibed water or other hypotonic liquids, and which in the second place protects the body fluids of the insect from extreme variations of concentration, variations which are not only undesirable but dangerous to it.