138 Organisms from Eggs 



This symmetry is probably due to the following fact : 

 the first cleavage plane goes through that spot where 

 the intestine grows into the blastula cavity. If the 

 micromere material does not change its position after 

 the two cleavage cells are separated and the new blas- 

 tulae do not become completely spherical the symmetry 

 which we observed is bound to occur. The occurrence 

 is a confirmation of Boveri's observation. It is natural 

 that Driesch also found that each cell in the four-cell 

 stage should give rise to a full embryo, since each of these 

 cells is in reality a diminutive egg containing the three 

 strata in the right arrangement. When, however, the 

 cells of the eight- or sixteen-cell stage were isolated 

 Driesch's results were different. In this case the isolated 

 cells from the ectoderm material did no longer all form 

 a gastrula; when such a cell still formed a gastrula it 

 was probably due to the fact that it contained some 

 entoderm material; while the cells taken from the 

 entoderm region all formed embryos and therefore 

 contained ectoderm material. ' The isolated ectoderm 

 cells of a blastula could no longer form an intestine; 

 they were lacking the entoderm material. It looks as 

 if a gradual migration of all the entoderm material 

 from the ectoderm into the entoderm took place during 

 the blastula formation. 



When the contents of the egg are displaced by pres- 

 sure the result will be determined by the location of 



' Driesch, H., Arch. f. Entwcklngsmech., 1900, x., 361. 



