Memoirs: The Formation of the Peritrophic Membrane in Insects, with Special Reference to the Larvae of Mosquitoes

Abstract

In the larvae of mosquitoes (Anopheles, Culex, and Aedes) the secretion from the cells of the cardia, in the proventriculus, is drawn through an annular press and thereby moulded to form the peritrophic membrane. The mechanism of this press has been described in detail. It seems probable that, throughout the Diptera, the peritrophic membrane is formed by similar mechanisms. Figures are given of those in the larvae of Sciara (Cecedomyidae), Rhyphus (Rhyphidae), and Telmatoscopus (Psychodidae). Analogous structures (a zone of secreting cells in connexion with an annular press) have been found in most of the main orders of insects, as follows : Hymenoptera [adult of Bombus and Apis and the larva of a saw-fly (Tenthredinidae)]; Coleoptera [larva of the mealworm (Tenebrio molitor) and the adult of Coccinella]; Lepidoptera [larvae of Cheimabacche fagella (Oecophoridae), Sitotroga cerealella (Gelechiadae) and Ephestia kuhniella (Pyralidae)]; Aphaniptera (larva of Ceratophyllus wickhami); Isoptera; Neuroptera (adult of Hemerobius); Odonata (larva of Aeschna); Orthoptera (Blatella germanica); and Dermaptera. In every case, in addition to its function as a press, the so-called ‘oesophageal valve’ was found to act not as a valve but as a sphincter. In the honey-bee (Apis), the larva of the dragon-fly (Aeschna), and possibly in other insects, indefinite membranes are shed off by the cells farther back in the mid-gut, and added to those produced in the annular press. In all the insects examined, chitin formed the basis of the peritrophic membrane. The observations recorded give a coherent significance to much of the previous work on the subject, which, before, appeared contradictory.