On the tissue isolated in some of the larval appendages of Sialis lutaria L. at the larval-pupal moult

Abstract

Blood and epidermal cells are isolated in the old cuticle during the larval-pupal moult and are shed with that cuticle. The cells are left behind in the isolated fluid, which is a mixture of moulting fluid and haemolymph. No cells have been observed in the moulting fluid at any other moult. The number of cells cut off seems to be directly proportional to the size of the larva and hence to the size of the structure withdrawn. The blood cells in the isolated fluid are capable of clotting and forming tanned wound plugs at a time when the haemolymph of the pupa scarcely clots. The activity of the blood cells within the isolated fluid declines with time. During the retraction of the epidermis in the gills, a new cuticle, or moulting membrane, is continuously secreted. Where this is exposed to activated moulting fluid it is dissolved immediately before the larval-pupal ecdysis except for the innermost layer, secreted immediately before the production of the new pupal cuticle. The latter layer envelops the whole body of the insect and seems to be homologous to the ecdysial membrane of other insects. The thick new cuticle within the gills does not appear to have any distinct functional significance for the pupa beyond protecting the retracting gill tip.