The ootheca is of interest because it is composed of quinone-tanned protein. No detailed account of the secretory processes leading to the production of structural protein and tanning agents exists, and this paper is intended as an introduction to such a cytological and histochemical account; it contains a description of the general anatomy of the organs concerned with the formation of the ootheca. These organs are located round the vestibulum, a large intucking of the posterior part of the abdomen.

The colleterial glands open into the vestibulum and secrete most of the protein and tanning agent. The structure of each type of secretory cell of which the gland is composed is outlined.

A new organ, taking the form of a large invagination of the dorsal wall of the vestibulum, is described. The walls of this invagination are secretory, and it is notable that the secretion-product accumulates and is stored within the substance ofa modified layer of the endocuticle.

Two types of massed dermal gland cells are described. One type is present mostly on the ventral walls of the ovipositor, and the other towards the posterior end of the vestibulum. The former may not be directly concerned with ootheca formation, while the latter probably secretes the alkali-resistant outer layer of the ootheca.

The relations between the ovipositor and the ‘horned die’ of Kramer and Wiggles-worth are discussed.

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