ABSTRACT
In a recent paper (Wigglesworth, 1932a) the theory was put forward that the chief function of the so-called rectal glands of terrestrial insects is the reabsorption of water from the excreta in the rectum, and it was suggested that many of the supposedly respiratory structures in aquatic insects, such as the anal gills of the mosquito larva (which may perhaps be looked upon as homologous with rectal glands that have prolapsed through the anus), might also be concerned in absorbing water, not from the excreta, but from the surrounding medium. It has been shown in another place (Wigglesworth, 1932b) that the properties of the anal gills are such that they must almost certainly absorb water, but in the present paper this hypothesis will be proved experimentally.
The tracheal supply of the anal gills is very sparse as compared with that of undoubted respiratory organs such as the tracheal gills of Ephemerid larvae or the skin of parasitic Hymenopterous larvae.
