of any movement, absence of mitosis (Slifer') and very low rates of respiratory metabolism (Bodine'). The third period begins with the resumption of mitotic activity followed by blastokinesis. After the embryo has revolved, it grows rapidly and engulfs the remaining yolk. The third phase marks the completion of differentiation and embryonic o rganogenesi s.This preliminary report on the glutathione reaction is based upon observations of 13 embryos in early development, 70 embryos in diapause, and 30 in various stages of later development. The nitroprusside test for -SH groups was used and the color lasted from 18 to 90 seconds. All embryos (even those in diapause) gave a definite positive color reaction. The stain was apparently more intense and lasting where the tissues were thicker. Yolk did not stain and embryonic membranes colored only momentarily. It is significant that embryos in all stages of diapause showed an intense color reaction indicating the presence of the protein bound -SH groups. It is possible that the -SH group relates more to potential cell activity, rather than indicating active cell division as postulated.

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