THE RELATION OF FAT CHANGES TO THE GENERAL CHEMICAL EMBRYOLOGY OF THE SEA URCHIN

¹ From the Zoölogical Laboratory, Dalhousie University, Halifax, Canada, and the Marine Biological Laboratory, Woods Hole, Mass.

Periodical estimations were made of the total fat, sterol and phospholipid during the first 40 hours of development of Arbacia. The total fat decreases up to the time of hatching (8 hours), then increases for some 10 hours, and later decreases again. The sterol concentration remains unchanged throughout the period studied. Owing to fluctuations in the phospholipid readings, a definite conclusion could not be drawn as to whether this material is utilized as a source of embryonic energy. The total fat in a million unfertilized eggs is 5.65 mg. of which 7.5 per cent is sterol and 38 per cent phospholipid. A general hypothesis of the chemistry of early sea urchin development is presented.