Histological structure of the seminal receptacle, sperm storage and utilization in the golden cuttlefish (Sepia esculenta)

The changes in the spermatozoa number in spermatangia and seminal receptacles at different times after copulation, and the structure of the seminal receptacle were examined by using experimental ecology and tissue section techniques to reveal the mechanism of sperm storage in seminal receptacle and sperm utilization during oviposition. The results showed that paired seminal receptacles were located in the raised ventral portion of the buccal membrane, and opened inside the buccal membrane. The entire seminal receptacle was connected by a central duct, which had many folds and cilia on its inner surface. Each seminal receptacle had 12-20 sperm storage bulbs surrounded by circular muscles. A large number of spermatozoa were stored in sperm storage bulbs, and the heads of most spermatozoa faced toward the inner surface of sperm storage bulbs. After one copulation, the utilization of spermatozoa in spermatangia and seminal receptacles could be divided into three stages: ① the utilization of spermatozoa mainly from spermatangia (1-2 d after copulation); ② the transition from the utilization of spermatozoa in spermatangia to spermatozoa in seminal receptacles (2-3 d after copulation); ③ the utilization of spermatozoa mainly from seminal receptacles (more than 3 d after copulation). These results suggest that spermatozoa released from the spermatangia reached the seminal receptacles through the folds on the surface of the female buccal membrane. Spermatozoa entered the sperm storage bulbs through self-movement and cilia fluttering on the inner surface of the central duct. The distribution of spermatozoa inside the sperm storage bulbs was highly regular, and the heads of most spermatozoa faced toward the inner surface of the sperm storage bulbs. During spawning, females preferred to use spermatozoa from spermatangia to fertilize their eggs. When spermatozoa in spermatangia were insufficient, spermatozoa in seminal receptacles were released gradually by muscle contraction and cilia fluttering, and ova were fertilized externally near the female buccal membrane.