The paper consisted of a detailed account of the external form; the arrangement of the body-cavity and its walls; the perivisceral space and corpuscles; the digestive, circulatory, and generative systems.

It was specially mentioned, in regard to the perivisceral corpuscles, that the author was not at all inclined to think that they originated from the glandular fatty coating of the digestive tract and the dorsal blood-vessel. The corpuscles seem rather to be the product of the perivisceral cavity itself and its special (free) contents. This view requires no stretch of ordinary physiological principles, and is quite in keeping with what is found in other groups. In the Nemerteans, for instance, a complex corpusculated fluid is produced within a closed chamber with smooth walls.