Quarterly Journal of Microscopical Science, Vol s2-79, 151-179, Copyright © 1936 by Company of Biologists

Memoirs: Internal Anatomy of a Caddis (Hydropsyche Colonica)

¹ Department of Entomology, Imperial College of Science and Technology

1. The main features of the anatomy and histology of the larva of Hydropsyche colonica, and of the gut, male reproductive organs, and nervous system of the adult are described.

2. The larval alimentary canal is comparable to that of Lepidoptera, but is peculiar in the possession of a gizzard, a special development of the oesophageal valve, and rectal gills. These peculiarities, however, are not general in caddises. The silk glands are on the whole similar to those of Lepidoptera, the most important difference being the reduction of Lyonet's gland. A new type of gland opening on the back of the head is described. The process of ecdysis is associated with extensive changes in the fore-gut.

3. There is no evidence that the adult takes food, and the fore-gut forms an air-sac. Eectal glands are present. The adult nervous system appears to have seven abdominal ganglia (eight in the larva) owing to the complete fusion of the metathoracic and first abdominal ganglia.

4. Before pupation, the prepupa almost halves its length by a muscular contraction which can be induced in the immature larva by certain conditions of fixation. The significance of this contraction is discussed tentatively.