'XL] PROBLEMS OF THE DAY. 93 



in order that the germ-plasm may become dominant. It is 

 possible that this explanation may be incorrect. The latest 

 observations on the conjugation of Infusoria, as recorded in the 

 excellent works of Maupas and R. Hertwig, are opposed to my 

 explanation, although the idea upon which it was formed is 

 justified. Since it is the nuclear substance which gives to the 

 cell its specific character, the egg-cell must before fertilization 

 be dominated by an idioplasm distinct from that of the sperm- 

 cell, for they are, up to this point, of different form and function. 

 As soon however as fertilization is accomplished they both 

 contain the same idioplasm, namely germ-plasm. Hence the 

 earlier dominant idioplasm must be different from the later. 



This fundamental idea upon which my interpretation of 

 the first polar body was founded appears to be sound. One 

 might perhaps imagine that the idioplasm of the Qgg was 

 originally different from that of the spermatozoon, but that both 

 possessed the power of changing into germ-plasm. But this 

 would leave wholly unexplained the fact that parthenogenetic 

 eggs extrude one polar body. Both facts become clear, if ova 

 and spermatozoa are dominated until they reach maturity 

 by different histogenetic idioplasmata, with which a small 

 amount of germ-plasm is mingled, and if when the former are 

 removed, the germ-plasm governs both cells. This process is in 

 no way extraordinary and unparalleled ; for entirely analogous 

 divisions of the idioplasm into halves of unequal quality, must 

 take place hundreds of times in every embryogeny. However, 

 I wilHngly admit that on this question the last word has not 

 yet been spoken, and would merely add that my theory of 

 heredity is not concerned thereby. As regards my theory, the 

 significance of the second polar body, and not that of the first, 

 is decisive. Even if it be demonstrated that my interpretation 

 of the first polar body is erroneous, this would not interfere 

 with the conception of the second as halving the number of 

 ancestral germ-plasmata. I should then look upon the first 

 division as merely leading up to the second, as a first step 

 necessary for the reduction of the ancestral plasmata, although 

 the reason for its necessity is not at present quite clear 

 to us. 



The occurrence of regular changes in the idioplasm during 

 ontogeny, which I have urged, and which has been attacked 



