Differences between male and female protogonia in chick embryos before sex differentiation of the gonads.

The sex of chick embryos is diagnosed by cyto-karyological methods on skin fragments of 2-7 days' incubation before gonadal sex differentiation. In 44 males and 42 females statistical analyses have been made of the number and dimension of the germ cells, and of the volume of the gonadal primordia. Moreover an ultrastructural study has been made on the germ cells colonizing the genital ridges (70-hours of incubation). Early differences between the sexes have been found regarding: earlier numerical increase of CGs in the left gonadal primordium of the females; larger primordial germ cells in the female; the same cytological characteristics at ultrastructural level.