1 86 Regeneration 



phenomenon of merogony was discovered by Boveri 

 and was elaborated by Delage. * 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. expSr., 1899, vii., 383. 

 •Driesch, H., Arch.f. Entwcklngsmech., 1905, xix., 648. 



