| Studies on histology of reproductive system and cell biology on spermatogenesis and oogenesis of Bullacta exarataying xue-ping(Department of Biological and Environmental Science, Wenzhou Normal College;Wenzhou 325027, China)Bullacta exarata belongs to Family Atyidae (Mollusk,Class Gastropoda,Subclass Opisthobranchia). Bullacta exarata is marine mollusk that has high nutrient vaule, and it also has high economic significance in the coastal southern of Zhejiang province. There are few reports about Bullacta exarata' reproductive biology. Only You zhong-jie et al.(1993> 1994) reported gonadic development and reproductive periods of Bullacta exarata. Transmission electron microscopy was used to study the morphological structures changes of nucleus and cell organelle during spermatogenesis and oogenesis of Bullacta exarata. The ultrastructure of spermatozoa morphology of Bullacta exarata was also analyzed, and the morphological structure of spermatozoa that is one of the important characters of reproductive evolution was discussed in this paper. The histological structure of reproductive system and gonadic development were studied too. Through this research, we not only accumulate the base date on artificial grow seedlings and exploit utilization of Bullacta exarata , but also enrich the reproduct biology of Mollusk Gastropoda. The main results are as follow: 1. The histological study of reproductive systemBullacta exarata is monoecism. It's reproductive system is composed of genital organ, copulatory pouch and ovarian groove. The genital organ includes ovotestis, hermaphroditic duct, semen bursa, albumen gland, mucous gland, nidamental gland, copulatory bursa and prostata. Ovotestis includes ovary and testis which in the center of ovotestis.The testis forms semen firstly. After reproductive cells are grown, it goesthrough hermaphroditic duct, then the male and female genital tract is separated, but go alone side by side, and eggs and spermatozoa enter them selectively. What in the end of hermaphroditic duct is copulatory bursa. It is the place of fertilization. In the adjacency of copulatory bursa is albumen gland and mucous gland, which secretes protein and mucus respectively and surround eggs. Copulatory pouch is composed of stimulatory organ and penis. Penis is after of stimulatory organ. They ranges parallel. Ovarian groove is formed from sunken skin, on the ovarian groove's wall there is ciliums. 2. SpermatogenesisSpermatogonium is oval or circular shaped, the chromatin begins to condense, and the karyotheca can be clearly observed. In this stage, there are few ribosome, golgi vesicle and a lot of mitochondria in the cytoplasm. Few endoplasmic reticulum distribute around the nucleus.In the stage of primary spermatocyte, the nucleus lie in one side of the cell. The chromatin is distributed hi granules or small conglomeration in the nucleus, and there is a high electron-density nucleolus in the nucleus. Cell organelle are in polar-distribution, mitochondria with developed ridges are plentiful. The number of golgi vesicle and ribosome is abundant in the cytoplasm. In the stage of second spermatocyte, the cell is smaller than primary spermatocyte, and the shape is elongated round. Double nucleus was always seen in this stage, and the polar-distribution of mitochondria is much more clear.Spermatids of Bullacta exarata are developed through the following three main stages, that is, the early stage, middle stage and end stage. During these series of proceeds, the inner changes in the spermatozoon cell can be described as foliows:(l)Changes in nucleus. The oval-shaped nucleus of early spermatid comprises heterogeneous aggregations of short silk-shaped chromatin, and part of vesicle may be seen on the karyotheca. In the middle stage of spermatid, the nucleus is kidney shaped, and the chromatin condenses to silk-shaped. As the spermatid matures, the nucleus elongates hi the anterior-posterior axis and the chromatin condenses to long thread, then condenses to high and even electron-density till...
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