1893. EXPERIMENTAL EMBRYOLOGY. 297 
which was only published (through Roux) towards the end of last 
year, is the more interesting since Ctenophora are far removed from 
Amphibia. In both cases there is unequal segmentation of the ovum, 
and in both cases the formation of the missing half is long delayed. 
IV. L. Chabry, experimenting with the ova ofan Ascidian (A scidia 
aspersa), obtained results which are, on the whole, similar to those 
of Roux. His method is to place the ovum in a glass tube, of almost 
equal diameter, and to puncture one of the first two segmentation- 
cells, observing it, meanwhile, under the microscope. The cell dies; 
the survivor forms a typical half-morula, half-gastrula, a right or a 
left half-larva. If the two anterior cells of the four-celled stage be 
destroyed, a posterior half individual results. Quarter and three- 
quarter forms were also obtained. Moreover, Chabry believes that 
he has been able to detect the cells whose descendants give rise to 
eye, notochord, attaching papillae, &c. On to the sixteen-cell stage, 
at least, each cell has a determined destiny, it represents a definite 
part of the embryo; if a cell be destroyed, the defect in the larva is a 
definite one. It may be noted that Roux does not think Chabry’s 
figures of half-gastrule really justify the title, it seems to him as if 
a regenerating process had already begun to operate so as to complete 
the embryo. There is not, however, any revitalising of the injured 
half-egg, for the injuries are fatal. 
V. Carl Fiedler (1891) experimented with the ova of Echino- 
derms (especially of Echinus microtuberculatus), first trying the puncturing 
method, afterwards following the Hert wigs’ method of shaking the eggs. 
When one of the first two segmentation-cells was punctured, so that 
it merely lost some of its substance, it did not die: it recovered and 
divided as usual, except that the cells to which it gave rise were 
smaller than those of the other side. The blastula was unsym- 
metrical, the embryo normal. But when one of the first two seg- 
mentation-cells was punctured so that the nucleus was fatally injured, 
the cell died; the surviving cell formed a half-morula, a half-blastula, 
and, perhaps, even a half-gastrula. When two cells of the four-cell 
stage were injured, a half-development also resulted, and that the 
same whatever pair of cells remained. Therefore, the first four cells 
are equivalent ; but at the eight-celled stage this equivalence is lost, 
for different groups of four turn out differently. 
VI. Hans Driesch (1891) also experimented with the ova of sea- 
urchins, pursuing the shaking method. When the first two 
segmentation-cells were shaken apart, one of them usually died, the 
survivor divided into a half-morula, as was the case in Fiedler’s 
experiments ; but the half-morula formed a closed blastula of less 
than the normal size. Then followed a small gastrula stage, and a 
minute Pluteus larva. Thus, from one of the first two segmentation- 
cells a normal but minute larva may develop. While Roux got half- 
embryos from half-an-egg, Driesch got half-sized but otherwise 
complete embryos. 
