Sex differentiation of somatic tissue in the unsexualised gonad primordia of the embryos of three species of poeciliid fish.

The structure of the gonad primordia is described in the embryos of three species of poeciliid fish. Prior to the sexualisation of the germ cells, a dimorphism exists based upon the gonadal somatic features. This serves as a basis for distinguishing between male and female specimens. Presumptive males are characterised by the presence in at least one of their gonad primordia of a conspicuous stalk whereas in presumptive females, a stalk is completely lacking.