Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). II. Annual oviducal cycle

This article is the first ultrastructural study on the annual oviducal cycl e in a snake. The ultrastructure of the oviduct was studied in 21 females o f the viviparous natricine snake Seminatrix pygaea. Specimens were collecte d and sacrificed in March, May, June, July, and October from one locale in South Carolina during 1998-1999. The sample included individuals: 1) in an inactive reproductive condition, 2) mated but prior to ovulation, and 3) fr om early and late periods of gravidity. The oviduct possesses four distinct regions from cranial to caudal: the anterior infundibulum, the posterior i nfundibulum containing sperm storage tubules (SSTs), the uterus, and the va gina. The epithelium is simple throughout the oviduct and invaginations of the lining form tubular glands in all regions except the anterior infundibu lum and the posterior vagina. The tubular glands are not alveolar, as repor ted in some other snakes, and simply represent a continuation of the oviduc al lining with no additional specializations. The anterior infundibulum and vagina show the least amount of variation in relation to season or reprodu ctive condition. In these regions, the epithelium is irregular, varying fro m squamous to columnar, and cells with elongate cilia alternate with secret ory cells. The secretory product of the infundibulum consists largely of li pids, whereas a glycoprotein predominates in the vagina; however, both prod ucts are found in these regions and elsewhere in the oviduct. In the SST ar ea and the anterior vagina, tubular glands are compound as well as simple. The epithelium of the SST is most active after mating, and glycoprotein vac uoles and lipid droplets are equally abundant. When present, sperm form tan gled masses in the oviducal lumen and glands of the SST area. The glands of the uterus are always simple. During sperm migration, a carrier matrix com posed of sloughed epithelial cells, a glycoprotein colloid, lipids, and mem branous structures surround sperm in the posterior uterus. During gravidity , tubular glands, cilia, and secretory products diminish with increasing de velopment of the fetus, and numerous capillaries abut the basal lamina of t he attenuated epithelial lining of the uterus. (C) 2000 Wiley-Liss, Inc.