The question of the number of cells which are produced by the one-half and one-fourth embryos had not up to this time been determined. Until this was known it could not be stated whether the smaller embryos were miniature copies of the normal embryos in all respects, or whether they assumed the typical form with fewer cells. I found (’95) that the blastula from one of the first two blastomeres contains half the number of cells produced by the whole embryo, and that in the later stages also it contains only about half the normal number. The one-fourth blastomere produces only a fourth of the whole number of cells, and yet can develop with this number, in many cases, into a whole embryo. The one-eighth blastomere produces one-eighth the normal number of cells. In most cases I found that these one-eighth blastomeres do not produce embryos, but occasionally they produce a gastrula, and probably a young pluteus stage. The development of nucleated fragments of the egg was also studied in order to find out if they too produce a smaller number of cells than does the whole egg, and a number in proportion to their size. The problem is different in this case, because the nucleus has not divided before the piece is separated, and the results ought to show whether there is a prescribed number of divisions for the egg nucleus, or whether the number of times it divides is regulated by the amount of the protoplasm. It was found that the number of cells produced by each fragment is in proportion to the size of the piece. This shows that the division of the nucleus is brought to an end when the protoplasm has become subdivided to a certain point. A further examination of the number of cells that are invaginated in these smaller “partial” larvæ to produce the archenteron seemed to show that they often use relatively more than their proportionate number. The normal blastula of _Sphærechinus granularis_ contains about five hundred cells and turns in fifty cells, or one-tenth the total number. The one-half and one-fourth embryos, and some of the small embryos from the egg fragments, seemed to invaginate more than one-tenth of their total number of cells.