Tracheal and Blood Gills in Aquatic Insect Larvæ

Abstract

AMONG the larvæ of aquatic insects, two fairly well-defined types of gill-like structures are commonly found—‘tracheal gills’ and ‘blood gills’. The former term is applied to thin plates or filaments with a copious tracheal supply and only a very small blood cavity, structures which are typically developed in such insects as Ephemeroptera and Trichoptera. The term ‘blood gill’ is restricted to organs which have a spacious lumen but in which tracheæ are poorly developed or totally absent; the ventral and anal gills of Chironomus being a familiar example. The work of Fox¹ on Chironomus gave rise to doubt as to the respiratory function of blood gills in general, doubt which has been strengthened by the confirmatory work of Harnisch², and in a recent series of papers Wigglesworth³ describes experiments upon the anal gills* of the larva of the yellow-fever mosquito (Aedes (Stegomyia) argentatus), from which he concludes that the main function of these structures is the absorption of water and that they are of little value as organs of respiration. Since in this species they are much larger than in the majority of allied forms, it is probably safe to assume that in the Culicidæ as a whole, anal gills are of little importance from the point of view of respiration : a conclusion which in confirmed by my own experiments on Culex spp.