Summary

1. In the course of an investigation on the phosphorus metabolism of the developing egg of Sepia, it was found that the embryo, but not the yolk, contains arginine phosphate at all stages.

2. The inorganic phosphate per unit weight of embryonic tissue rises continually throughout development, but the inorganic phosphate per unit weight of yolk rises to a maximum early in development and falls thereafter to a constant level.

3. The arginine phosphate of the embryo, expressed as per cent. of the total inorganic and labile water-soluble phosphorus, rises to a maximum at embryo weight 95 mg. (86 days' development) and then falls to the adult level by the time of hatching. It is suggested that this reflects in chemical terms the attainment of maximal relative weight of the muscle masses during development.