“On chemical fertilization”

1. In two previous publications the author mentioned the fact that by applying two different methods of treatment to the unfertilized egg of the sea urchin, this egg could be caused to develop in a way which resembled in all its essential features the development of the eggs fertilized with sperm. These two methods consisted, first, in putting the eggs for about two hours in hypertonic sea water (the method used in the early experiments) and, second, in exposing the eggs for from one to two minutes to sea water, to which a certain amount of acetic acid or formic acid had been added. When the old method alone was used the eggs did not form a membrane, nor did the larvas rise to the surface. When the acid treatment alone was used, the eggs formed a membrane and after about six hours divided into from two to six cells, but then died. When the eggs were exposed to the acid for only a short time, e. g., for three-fourths of a minute, not all the eggs formed a membrane when put back into normal sea water; and in this case only those divided into two or four cells and subsequently died within 20 hours, which had formed a membrane, while those eggs which had not been exposed long enough to the acid to form a membrane neither segmented nor died. If both methods of treatment were combined, however, those eggs which had formed a membrane developed at about the same rate as the eggs fertilized with sperm. A certain percentage of these eggs rose to the surface of the water in the usual way, while the eggs which had not formed a membrane either did not develop at all, or developed in the somewhat abnormal and slow way characteristic of the treatment by hypertonic sea water alone.