In all the preceding cases in which the blastomeres have been _separated_, a whole embryo has developed, although the cleavage was often like that of a part. In one form, however, it has been found that a whole embryo does not develop. Chun (’92) first showed that the isolated one-half blastomere of the ctenophore egg produced a half-larva. He also inferred from certain incomplete embryos caught in the sea, that these incomplete larvæ could subsequently regenerate the missing parts. Driesch and Morgan (’95) studied the development of the isolated blastomeres of another ctenophore, _Beroë ovata_. They found that the isolated one-half blastomere divides exactly as a half of the whole egg (Fig. 66, _A_, _B_, _C_). It remains more or less a half-structure, even after the ectoderm has grown over the whole surface (Fig. 66, _D_). The invagination of ectoderm, to form the so-called stomach, that takes place at the lower pole of the whole embryo, is formed at one side of the lower pole in the half-embryo (Fig. 66, _F_, _G_). It pushes into the endodermal yolk mass, and lies not in the middle, but somewhat to one side. In the normal embryo there are formed four endodermal sacs or pouches in the central yolk mass that become connected with the inner end of the ectodermal stomach, around which they lie symmetrically. In the half-embryo two sacs are formed, and in addition a smaller third sac, which always lies on the side of the stomach that is nearest the outer wall (Fig. 66, _F_, _G_). The embryo is, therefore, somewhat more than half the normal embryo in regard to the number of its endodermal sacs. There are present eight meridional rows of paddles in the normal embryos of the ctenophore. They lie symmetrically on the sides, converging towards an apical sense organ. In the one-half larva there are always only four of these rows of paddles that are not equally distributed over the surface, since on one side there is a wider gap between two of the rows than elsewhere (Fig. 66, _G_). The sense plate also lies somewhat eccentrically, _i.e._ more towards the side corresponding to that at which the other blastomere lay. If the one-fourth blastomeres are separated, each continues to segment as though still a part of the whole. A one-fourth embryo develops that has an unsymmetrical stomach, with _two_ endodermal sacs. There are only two rows of paddles. The embryos are, therefore, in several respects one-fourth embryos, but the presence of two endodermal sacs, instead of only one, shows that in this particular, at least, the embryo is more than a fourth of the whole.