346 ON THE NUMBER OF POLAR BODIES AND 



to it depended, as far as they went into details, upon assumptions ; 

 but the fundamental view that the quantity of the nucleus decides 

 whether embryonic development takes place with or without fer- 

 tilization seemed to me, even at that time, to be correct, and to be 

 a conclusion required by the facts of the case. Indeed, I thought 

 it not unlikely that its validity might be proved by direct means : 

 I pointed out that a comparison of the quantities of the nuclei in 

 parthenogenetic and sexual eggs, if possible in the same species, 

 would enable us to decide the question (/. c., p. 234). 



I had thus set myself the task of making this comparison. The 

 result of this investigation was to show that, as already mentioned, 

 polar bodies are formed in parthenogenetic eggs. But even the 

 first species successfully investigated revealed a further fact, which, 

 if proved to be wide-spread and characteristic of all partheno- 

 genetic eggs, was certain to be of extreme importance : the matura- 

 tion of the parthenogenetic egg is accompanied by the expulsion of 

 one polar body, or, as we might express it in another way, the 

 substance of the female pronucleus is only once divided, and not 

 twice, as in the sexual eggs of so many other animals. If this 

 difference between parthenogenetic and sexual eggs was shown to 

 be general, then the foundations of my hypothesis would indeed 

 have been proved to be sound. The quantity of nuclear substance 

 decides whether the egg is capable of undergoing embryonic 

 development. This quantity is twice as large in the partheno- 

 genetic as in the sexual egg. I had, however, been mistaken in 

 a matter of detail ; for the difference in the quantities of nuclear 

 substance is not produced by the expulsion of two polar bodies, and 

 the reduction of the nuclear substance to a quarter of its original 

 amount, in both eggs, while the parthenogenetic egg then doubles 

 its nuclear substance by growth ; but the difference is produced 

 because the reduction of nuclear substance originally present is less 

 in one case than it is in the other. In the parthenogenetic egg 

 the nuclear substance is only reduced to one-half by a single 

 division ; in the sexual egg it is reduced to a quarter by two 

 successive divisions. It is an obvious conclusion from this fact, if 

 proved to be wide-spread, that the significance of the first polar 

 body must be different from that of the second. Only one polar 

 body can signify the removal of ovogenetic nucleoplasm from the 

 mature egg, and the second is obviously a reduction of the germ- 



