Eggs of Xenopoecilus sarasinorum possess two distinct types of filaments on the surface of the egg envelope (chorion), long, attaching filaments restricted to the vegetal pole and weak, nonattaching filaments around the animal pole (micropyle). Both types are formed during oogenesis. After mature eggs were spawned through the urogenital pore, they were fertilized and hung in an abdominal concavity of the female. Oviposition never took place in the presence of embryos in the concavity because of the retardation of oogenesis. The loosely tangled tips of the attaching filaments that are retained within the ovarian cavity plug the urogenital pore by forming a hard complex with the epithelial cells. Into this plug structure that fuses with the inner wall of the urogenital pore, capillaries are provided. Within 5 days after the initiation of hatching, this plug degenerates and is released from the urogenital pore. Thus, in female X. sarasinorum, the reproductive cycle seems to be regulated by the physiological function ofthe plug structure formed by the attaching filaments in response to the presence of developing embryos.

To investigate the internal fertilization of the guppy Poecilia reticulata, the present electron microscopic observations were focused on the morphology of the sperm storage site in females. In the ovary of the mature female guppy, many spermatozoa were found in a synaptic knob-shaped micropocket (SSP) as the sperm storage (probably sperm entry) site on the follicle surface which was the expanded blind alley of a small tract extending from the ovarian cavity. Oocytes in the developmental stage of oil droplet formation already showed the attachment of the terminal end of the small tract opening into the ovarian cavity. The lateral wall of the tract attaching to the follicle surface consisted of epithelial cells fast jointed with tight junctions and desmosomes. The thick lateral wall of SSP was constructed with complex epithelial cell layers, and the terminal bottom was comprised of a single layer of epithelial cells on the surface of the follicular layer, which consisted of a very thin thecal cell layer, basement membrane, and granulosa cell layer. The vitellus was enclosed by the follicular layer and thin chorion, in which the micropyle was absent. In fully-grown oocytes, the germinal vesicle containing comparative short chromosomes did not always locate in the vicinity of the storage SSP of spermatozoa.

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