LIMITS OF DIVISIBILITY OF LIVING MATTER 333 



be the case to a sufficient extent to interfere with the devel- 

 opment. Fertilized eggs of Arbacia were kept in normal 

 sea-water until they had reached the eight-, sixteen-, and 

 thirty-two-cell stages, when the eggs were put into water 

 which had been diluted to a sufficient extent. The mem- 

 brane burst, and a portion of the egg contents flowed out, as 

 in the case of the unfertilized egg, only with this difference, 

 that in this case the extraovate consisted of a larger number 

 of cells. Nevertheless, the result was the same as in eggs 



7 oo 



which were made to burst before cleavage had begun. When 

 the separated pieces were sufficiently large greater than 

 one-eighth of the entire mass of the egg they developed 

 into a pluteus; when they were smaller than this, they 

 reached only the gastrula or blastula stage. If a differen- 

 tiation had occurred in the eight-cell stage, so that the 

 individual cells could give rise only to certain tissues, or- 

 gans, or regions of the body, we would expect that, when 

 only about eight of the cells from an egg in the thirty- two- 

 cell stage were separated from the main mass, we should 

 obtain only a conglomeration of different fragments of tis- 

 sues, organs, etc., but not an entire embryo, which is, how- 

 ever, not the case. It may also happen, as I have just 

 mentioned in the case of the uncleaved eggs, that the cells 

 in their sliding motions distribute themselves so that they 

 do not form a blastula ; but this does not occur of tener in 

 these eggs than in those which were ruptured before cleav- 

 age began. 



8. After this digression we will return to our main 

 theme, and ask the question whether it makes any difference 

 what portion of the protoplasm is cut out of an egg. It 

 might be that the egg is not completely isotropic. The 

 protoplasm always begins to flow out at the point at which 

 the membrane is ruptured. It can easily be shown, how- 

 ever, that the seat of the rupture may be at any point in the 



