1 86 Regeneration 



phenomenon of merogony was discovered by Boveri 

 and was elaborated by Delage. 1 Boveri, in comparing 

 the final size of the cells in normal and merogonic eggs 

 after the cell divisions had come to a standstill, found 

 that this size is always in proportion to the original 

 mass of the chromatin contained in the egg ; the cells of 

 the merogonic embryo, e. g., the mesenchyme cells, are 

 only half the size of the same cells in the normally 

 fertilized embryo. Driesch furnished a further proof 

 of Boveri 's law, that the final ratio of the mass of the 

 chromatin substance in a nucleus to the mass of proto- 

 plasm is a constant in a given species. Driesch com- 

 pared the size of the mesenchyme cells in a sea-urchin 

 embryo produced by artificial parthenogenesis with 

 those of a normally fertilized egg and found them half 

 of the size of the latter. When the fertilized eggs and 

 the parthenogenetic eggs are equal in size from the 

 start, which is practically the case if eggs of the same 

 female are used, the process of the formation of 

 mesenchyme cells comes to a standstill when their 

 number in the normally fertilized eggs is half as large 

 as the final number in the parthenogenetic egg. 2 

 Boveri's results as well as those of Driesch were ob- 

 tained by counting the cells formed by eggs of equal 

 size and not by simply measuring the size of the cells. 

 It is most remarkable that certain apparent exceptions 



1 Delage, Y., Arch. Zool. exper., 1899, vii., 383. 



8 Driesch, H., Arch./. Entwcklngsmech., 1905, xix., 648. 



