82 The American Naturalist. 





In all these cases the author will not grant that any true regeneration 

 of lost parts takes place. 



In the course of his discussion of the influence of yolk upon gastrula- 

 tion Paul Samassa" states that he has performed the following ex- 

 periments upon frogs' eggs. 



The eggs were injured, without breaking the egg membrane, by an 

 induction shock applied from needle points to certain cells or groups of 

 cells in the eight-cell stage of cleavage. 



When the four vegetative cells are injured there may result a cell 

 mass lying in two layers upon a mass of yolk and evidently represent- 

 ing, as seen in actions, a normal gastrula minus parts of its ectodermal 

 structures. On the other hand injury to the animal cells results in a 

 mass of cells lying near an inert mass of matter and possibly repre- 

 senting only entodermal cells. 



These facts are interpreted as meaning that the animal or the vegeta- 

 tive cells may continue their development for sometime independently 

 of life, or at least of the perfect state, of the other cells. 



These eggs die without reforming the injured parts by post- 

 generation. 



In an extensive theoretical part of the paper the author places him- 

 self in the main, on the side of Hertwig as believing in epigenesis rather 

 than in any form of preformation. 



The last paper that we can notice here is that of Amedeo Hekl- 

 izka 12 who succeeded in tying a thread about the eggs of Triton crista- 

 tus in such a way as to completely separate the first two cleavage cells. 



Hertwig compressed eggs by this method so that they formed hour- 

 glass shaped masses a single embryo finally resulted. 



But in these experiments where the egg is separated into two distinct 

 halves each develops by itself. From one half of the egg there results 

 an embryo that may live to have a medullary tube and a notochord. 

 This embryo was formed by a process of cleavage like that of an entire 

 egg and not like the cleavage of half an egg. 



The author holds that neither Weismann's nor any other ideas of pre- 

 formation will suffice to explain such phenomena, but that we must 

 accept some form of epigenesis. 



He thinks that each of the first two cells is totipotent and normally 

 makes half of the embryo when in the normal union with its fellow be- 

 cause of some inhibition of its power to produce the whole. In a case 

 of postgeneration we might suppose that this inhibition was removed 

 for a while and then resumed. 



