RECENT RESEARCHES ON OOGENESIS, 601 
ments to form the first true polar cell, at the same time the 
stimulated protoplasm contracts to eject some of the male 
element. If in the first division of the nucleus the male 
element be sufficiently got rid of, the process ends and the 
nucleus sinks back, if not a second polar cell is formed. The 
polar cell being mostly male disintegrates, though the presence 
of some lecithin or nutritive material may enable it to divide 
into isolated pieces; the ovum does not divide, for it has got rid 
of all the male substance which alone could render a parthe- 
nogenetic division possible. 
In his suggestive observation on polar cells, Bauchkanalzellen, 
and extrusions of other kinds from reproductive cells, Stras- 
burger (4) refers these phenomena to the necessity of securing 
for the differentiating reproductive nucleus a definite cyto- 
plasmic medium. The expulsion of the polar cell he is inclined 
to regard as a separation of part of the nutritive plasma, 
insisting that there is here no separation of male elements, 
since the results of indirect nuclear division are always two 
exactly similar twin daughter nuclei. He maintains that the 
differentiation of ovum or sperm nuclei is not effected by the 
extrusion of specific elements, but on certain modifications of 
the nuclear substance, and on certain nutritive conditions 
between cytoplasma and nuclei, which may be in some cases 
achieved by an elimination of portions of either. 
The last-developed theory of polar cells is due to Weismann 
(1), who brings the phenomena into relation with his theory of 
the continuity of the germ plasma. Starting from the concep- 
tion that the ovum is a histologically differentiated, nutritive- 
glandular cell, which must have a specific nuclear, histogenetic, 
or ovogenetic plasma besides the germ plasma, he maintains that 
the former predominates in the young ovum, while the latter is 
present only in small though increasing quantity. That the 
germ plasma may predominate and the development begin, some 
of the ovogenetic plasma must be removed from the ovum, and 
generally is, in the two successive cells divisions which give 
rise to the polar cells. He denies that the polar cells represent 
male elements (Minot and Balfour), but maintains that more 
