i. The Male Genital Ducts

The male duct is divided into a closed posterior region, the gonadial duct, which receives tributary ductules from the testis, and a long seminal groove running forward along the right side of the trunk, and continuing to the tip of the cephalic penis. The gonadial duct is

wide and thin-walled, running along the concave surface of the visceral mass, immediately beneath the renal organ, and distended throughout the year in the adult with seminal fluid, to form a close mass of opaque white convolutions. It functions as a vesicle for the storage of sperm, and is lined with short-celled cubical epithelium, with an underlying white fibrous coat. Eupyrenic sperm heads become periodically attached in a continuous row to the epithelium, and various stages of sperm disintegration are found within the cytoplasm.

The gonadial duct opens into the seminal groove at the posterior end of the mantle cavity. The first portion of the groove, about 1 cm. in length, represents a “prostate” of very elementary character, of the type described in primitive mesogastropods by Fretter (1946). It is bounded by tall folds of the pallial wall and the floor is thrown into several smaller epithelial ridges. The lining cells are columnar (20μ) with a dense coat of fine cilia reaching 12μ in height. There are frequent gland cells with darker staining basal nuclei and clear, non-staining secretion contents. Subepithelial glandular lobes as found in the prostate of more advanced mesogastropods are not developed. The seminal groove anterior to the prostate is enclosed beneath the right margin of the integumentary food groove. Gland cells are here less frequent, and the columnar epithelium shorter, though the cilia remain equally long. The penis is a long, recurved column, rather flattened, which in the adult may reach a length of 6 cm. In the immature animal it is a small pointed papilla.

An interesting feature in the Struthiolariidae is the extreme development of sperm dimorphism. The eupyrenic sperms, which are much the more numerous, are typical in appearance, with deeply staining rod-like heads (8μ) and long flagella (40–50μ). The oligopyrenic or vermiform sperms are giant cigar-shaped structures in Struthiolaria, 95μ–100μ in length. In Pelicaria they are shorter (50μ) and of curved, falciform shape. They progress by regular undulating waves of the flattened-marginal membrane, and appear to be formed by the elongation of spermatocytes that have lost their chromatin by unclear disintegration.