CH. XI] EFFECT OF INJURING A BLASTOMERE 121 



The lialf -embryos and the ivhole embryos of half-size developed 

 independently of the yolk-mass of the injured side. In this 

 respect my results differed very materially from the results of 

 Hertwig. Many of Hertwig's embryos developed in connection 

 with the injured blastomere ; mine, on the contrary, developed 

 independently of the injured blastomere. I suspect, as I have 

 said, that this difference may be in part due to this, that Hert- 

 wig did not carefully remove from his experiment those eggs 

 in which the injured blastomere continued to segment, and that 

 cells from the injured blastomere took a direct part in the sub- 

 sequent development. 



In one of my experiments, in which the uninjured blasto- 

 mere had been reversed after the operation, it developed into a 

 half-embryo, and not into a whole embryo of half-size. More- 

 over, in this embryo the medullary folds appeared on the white 

 surface of the egg, showing that a rotation of the contents of 

 the blastomere must have taken place. We must, therefore, 

 conclude that the simple fact of the rotation of the blastomere- 

 contents is not, in itself, the determining factor as to whether 

 a whole or a half -embryo will result, but probably the kind of 

 rotation determines this result. The result may also depend 

 in part, I think, upon how far the contents of the uninjured 

 blastomere have retained, after the operation, their organic 

 connection with the other injured blastomere. 



In later papers Roux stated that he has often obtained in his 

 experiment other sorts of embryos than those he first described, 

 which he calls "hemiooholoplasten/' These are whole embryos 

 that have come from the uninjured blastomere without the 

 postgeneratioii of the other injured blastomere. Roux inter- 

 prets these as embryos "completely postgenerated," with only 

 a partial use of material from the other side, or even with no 

 material from the injured side. Roux affirms that he has seen 

 all intermediate stages between those embryos that have used 

 all of the yolk-material of the injured side, those that have used 

 only a part of the material of the injured side, and those that 

 have not used any of this material. These embryos differ from 

 one another only in point of size. Roux does not call the em- 

 bryos that have developed entirely from the material of the 



