Early aspects of sex differentiation in the gonads of chick embryos.

In chick embryos whose sex had been previously identified by cytokaryologic methods, a light-microscope study of the number and dimensions of the germ cells (GCs) has been made from 2 to 7 days of incubation. Early differences between the sexes have been found. In females the GCs were larger and increased in number earlier than in males. This suggests an earlier differentiation of GCs in females. On the other hand, ultrastructural observations on GCs at 70 h incubation (colonization stage of the genital ridges) have revealed that male and female GCs differ from each other mainly in the amount of rough and smooth endoplasmic reticulum, mitochondria, glycogen particles and lipid droplets. This suggests early morpho-functional differences between male and female GCs.