AN AUTORADIOGRAPHIC INVESTIGATION OF THE GONADS OF THE PURPLE SEA URCHIN (STRONGYLOCENTROTUS PURPURATUS)

Abstract

1. The DNA-synthesizing cells in the gonads of the purple sea urchin were labeled with tritiated thymidine and detected with autoradiography.2. Some fibroblasts in the connective tissue-muscle layer and some cells of the visceral peritoneum covering the gonads synthesize DNA.3. Some of the non-germinal cells (the nutritive phagocytes) of the germinal layer proliferate during the spring and early summer, but proliferation ceases in the late summer as the nutritive phagocytes begin to accumulate cytoplasmic globules of reserve. Nutritive phagocytes labeled with tritiated thymidine in their deglobulated phase in the spring are still labeled up to several months later, after they have acquired cytoplasmic globules.4. In the testes of male urchins at the beginning of the reproductive season, not only relict spermatozoa, but also some newly-formed spermatozoa are ingested by the nutritive phagocytes. The phagocytosis of newly-formed spermatozoa ceases later in the reproductive season, at approximately the same time that spermatozoa begin to accumulate in the lumen.5. In the germinal epithelium of the testis, the germ cells which synthesize DNA are the spermatogonia and primary spermatocytes. Primary spermatocytes labeled with tritiated thymidine differentiate into early spermatids in about six days, while spermiogenesis takes approximately four days.6. Throughout the portion of the annual reproductive cycle when spermatozoa are being produced (August through March), the time course for the later events of spermatogenesis remains constant. Therefore, the events which control the rate of sperm production must occur early in spermatogenesis.7. In the germinal layer of the ovary, the germ cells which synthesize DNA are the oogonia and the pre-leptotene primary oocytes. During the same annual reproductive cycle, long-term experiments failed to demonstrate the differentiation of pre-leptotene primary oocytes into growing primary oocytes, maturing oocytes or ova. Therefore, it is likely that labeled primary oocytes remain small and inconspicuous until the following annual reproductive cycle when they grow and mature into ova.8. The sex of very small, immature urchins may be determined by histological examination of their gonads. The ovaries of immature female urchins contain small primary oocytes which are presumably the source of ova developing during the first annual reproductive cycle.