AUGUST WEI S MANN 347 



fication of histogenetic nucleoplasm, which may be called ovogenetic 

 nucleoplasm. This substance must greatly preponderate in the young 

 egg-cell, for, as we have already seen, it controls the growth of the 

 latter. The germ-plasm, on the other hand, can only be present in 

 minute quantity at first, but it must undergo considerable increase 

 during the growth of the cell. But in order that the germ-plasm may 

 control the cell-body, or, in other words, in order that embryonic 

 development may begin, the still preponderating ovogenetic nucleo- 

 plasm must be removed from the cell. This removal takes place in 

 the same manner as that in which differing nuclear substances are 

 separated during the ontogeny of the embryo : viz., by nuclear divi- 

 sion, leading to cell-division. The expulsion of the polar bodies is 

 nothing more than the removal of ovogenetic nucleoplasm from the 

 egg-cell. That the ovogenetic nucleoplasm continues greatly to pre- 

 ponderate in the nucleus up to the very last, may be concluded from 

 the fact that two successive divisions of the latter and the expulsion 

 of two polar bodies appear to be the rule. If in this way a small 

 part of the cell-body is expelled from the egg, the extrusion must in 

 all probability be considered as an inevitable loss, without which the 

 removal of the ovogenetic nucleoplasm cannot be effected. 



ON THE NATURE OF PARTHOGENESIS 



It is well known that the formation of polar bodies has been repeat- 

 edly connected with the sexuality of germ-cells, and that it has been 

 employed to explain the phenomena of parthenogenesis. I may now 

 perhaps be allowed to develop the views as to the nature of partheno- 

 genesis at which I have arrived under the influence of my explana- 

 tion of polar bodies. 



The theory of parthenogenesis adopted by Minot and Balfour is 

 distinguished by its simplicity and clearness, among all other interpre- 

 tations which had been hitherto offered. Indeed, their explanation 

 follows naturally and almost as a matter of course, if the assumption 

 made by these observers be correct, that the polar body is the male 

 part of the hermaphrodite egg-cell. An egg which has lost its male 

 part cannot develop into an embryo until it has received a new male 

 part in fertilization. On the other hand, an egg which does not expel 

 its male part may develop without fertilization, and thus we are led 



