344 ON THE NUMBER OF POLAR BODIES AND 



hypotheses are not strictly opposed to each other ; for the former 

 is a purely physiological, the latter a purely morphological ex- 

 planation. I desire to lay especial stress upon the fact that my 

 hypothesis is simply a logical consequence from the conclusion that 

 the nuclear substance determines the nature of a cell. How this 

 takes place is quite another question, which need not be discussed 

 here. If it is only certain that the nature of a cell is thus deter- 

 mined, it follows that a cell with a certain degree of histological 

 specialization must contain a nucleoplasm corresponding to the 

 specialization. But the mature egg also contains germ-plasm, and 

 there are only two possibilities by which these facts can be 

 explained : either the ovogenetic nucleoplasm is capable of re- 

 transformation into germ-plasm, or it is incapable of such re-trans- 

 formation. Now, quite apart from the arguments which might be 

 advanced in favour of one of these two possibilities, the fact that 

 a body is undoubtedly expelled from the mature egg seems to me 

 of importance, while it is of even greater importance that this body 

 contains nucleoplasm from the germ-cell. 



It may be thought that the process, as supposed by me, is 

 without analogy, but such a conclusion is wrong, for during every 

 embryonic development there are numerous cell-divisions in which 

 unequal nucleoplasms are separated from one another, and in all 

 these cases we cannot imagine any way in which the process can 

 take place, except by supposing that the two kinds of nucleoplasm 

 were previously united in the mother-cell, although their differ- 

 entiation probably took place only a short time before cell-division. 

 Perhaps the new facts which will be mentioned presently, and the 

 views derived from them, will make my hypothesis upon the histo- 

 genetic nucleoplasm of the germ -cells appear in a more favourable 

 light to the authorities above-named. 



My hypothesis has at all events the one merit that it has led 

 me to fruitful investigations. 



If the formation of polar bodies really means the removal of ovo- 

 genetic nucleoplasm from the mature egg, they must also be found 

 in parthenogenetic eggs ; inasmuch as the latter possess a specific 

 histological structure equal to that found in eggs requiring fertiliza- 

 tion. If, therefore, it were possible to observe the formation of polar 

 bodies in eggs which develope parthenogenetically, such an observa- 

 tion would not form a proof of the validity of my interpretation ; but 



