Physa fontinalis is a hermaphrodite gastropod in which the gametes formed in the ovotestis pass down the common hermaphrodite duct to the albumen gland, where the male and female systems separate. The spermatozoa are carried down the vas deferens to the penis and are introduced into the bursa copulatrix of the copulatory partner, whilst the eggs, after fertilisation, pass through the oviduct, where they receive the mucous coverings which form the egg capsule.
The morphology and histology of the reproductive system of P. fontinalis have been described, together with an account of the role of each of the genital organs. When mature, the spermatozoa are liberated from the ovotestis and are stored in the hermaphrodite duct, whereas, the eggs are released only immediately before oviposition and pass through the mass of male gametes. It is suggested that the muscle sheath which surrounds the junction of the hermaphrodite duct, vas deferens and oviduct constitutes a regulating mechanism, directing the ova and the majority of the spermatozoa into their correct channels.
The vas deferens is a ciliated, non-glandular duct, but the semen receives secretory additions formed by the prostate follicles, the glandular products being driven out of these diverticula by the action of small, interstitial, ciliated cells. During the breeding season, the characteristic, glandular cells in the penis sheath and praeputial gland become greatly swollen and secrete mucopolysaccharides which probably facilitate the eversion of the penis.
The female duct is composed of a glandular oviduct and muscular vagina, the former being divisible into three regions. The bursa copulatrix serves as a receptacle for foreign sperm and its duct opens into the vagina. Unlike the representatives of the other families of the Hygrophila which have been studied, a true albumen gland duct is missing and the ova pass into the albumen gland before entering the oviduct.
In P. fontinalis fertilisation occurs in the lower part of the hermaphrodite duct and not in the “fertilisation pockets”. It appears that the animal is largely self-fertilising, but it is suggested that after several generations have been produced by this means, a physiological barrier to the animal's own sperm is developed, so permitting fertilisation by foreign sperm.
The albumen gland secretes galactogen and, after fertilisation, the ova enter this organ to receive a coating of its nutritive secretion. As the eggs pass down the oviduct, they are surrounded by the mucous envelopes which constitute the egg capsule, each portion of the duct having a separate function in the formation of the different investments.