(ACTORS CONCERNED IN* THE PRODUCTION OF MITOSIS. 39 



forms consists in the modification of the rate of the process of 

 mitosis. 



3. The direct control of the mitotic process must be sought in 

 the chemical activity going on within the cells of the developing 

 individual. 



4. Experimental evidence indicates that with each cleavage of 

 an egg with determinate cleavage there is retained a definite 

 relationship between the number of any given cleavage and the 

 total number of cleavages that the embryo would undergo even 

 in those cases where the blastomeres become isolated in t he- 

 early stages of development. 



5. The foregoing would indicate clearly that within the cells 

 derived from the fertilized egg there are present factors or 

 potencies which exert direct control over the number of mitotic 

 divisions which shall ensue. 



6. The fact that not all of the blastomeres of the early cleavages 

 produce the same number of cells indicates that the number of 

 cells produced must be controlled by conditions developing as 

 the process of development progresses rather than by the parti- 

 tion and distribution of some definite materials present in the 

 egg at a time prior to the first cleavage. 



7. In tissues which retain the power of continued mitotic 

 division, as for example in the formation of the germ cells and 

 in tissues which have widely varying numbers of cells, the expla- 

 nation of the inconstant nature of the numbers of cells produced 

 may be sought in the acquisition of the power of eliminating 

 from the cell those materials which in the course of the process 

 of metabolism tend to accumulate and serve as inhibitors to the 

 mitotic process. 



LITERATURE CITED. 



Davenport, C. B. 



'08 Experimental Morphology. New York. 

 Driesch, H. 



'98 Von der Beendigung morphogener Elementarprocesse. Arch. f. Entw.- 

 mech., 6: 198-227. 



'oo Die isolirten Blastomeren des Echinidenkeimes. Arch. f. Entw.-mech., 



10: 361-410. 

 Loeb, J. 



'06 The Dynamics of Living Matter. Columbia U. Biol., Ser. VI 1 1. 



'12 The Mechanistic Conception of Life; Biological Essays. Chicago. 



