GERM CELLS AND SEX DIFFERENTIATION IN LEBISTES RETICULATUS

¹ WESLEYAN UNIVERSITY

1. The history of primordial germ cells in Lebistes reticulatus has been traced from the early gastrula (embryonic shield) until they become definitive germ cells in the ovary and testis.

2. When first observed, the primordial germ cells are scattered irregularly in the mesentoderm.

3. The formation of the medullary plate separates the germ cells into two lateral groups which become again more widely separated by the formation of somites and lie in the lateral mesoderm.

4. By the 2.7-mm. stage the germ cells are located in a median strand dorsal to the gut. Slightly later (3.1 mm.) they move laterally to the genital ridges.

5. Visible sex differentiation of gonads occurs shortly before birth (6 mm.).

6. The evidence indicates that primordial germ cells give rise to definitive germ cells. There is slight evidence that stroma cells may also give rise in the female to definitive germ cells. No such evidence has been found in the male.

7. Divergence in size between the sexes occurs about 35 days after birth and the first appearance of markings on the male at 48 days. This is coincident with a period of rapid multiplication of spermatogonia and progress of growth stages of spermatogenesis. No correlation with multiplication of interstitial cells has been observed.