Changes in the content of cyclic AMP and cyclic GMP in eggs of Mactra solidissima during the second cleavage cycle.

The levels of cyclic AMP and cyclic GMP during the second cleavage cycle of eggs of Mactra solidissima have been measured. Cyclic GMP levels vary reciprocally with cyclic AMP levels, the cyclic GMP level increasing up to 4 to 5-fold and the cyclic AMP level falling to 50 percent at the onset of mitosis.