RECENT RESEARCHES ON OOGENESIS. 597 
cell, just as has been maintained in regard to the ovum. It 
has been lately attempted to carry the comparison further by 
collating different forms of spermatogenesis with different modes 
of ovum segmentation. 
If any process in spermatogenesis can be morphologically as 
well as physiologically compared with polar cell-formation, these 
must occur in the mother-sperm cell or spermatogonium, while 
other phenomena observed in the spermatocytes or undifferen- 
tiated sperms may admit of physiological comparison. In their 
account of the spermatogenesis of Ascaris megalocephala, 
van Beneden and Julin (5) describe in the region where the 
spermatogonia are formed at the expense of their mother-cells 
or spermatomeres, certain corpuscles which they compare to 
polar cells. Two of these *‘ residual globules” are, according 
to them, expelled by the spermatomeres during their nuclear 
metamorphosis preceding division, and they believe that the 
expulsion is made in a manner similar to that in which they 
maintain that polar cells are formed, so that there is an actual 
extrusion of half the elements of the nuclear plate. This pro- 
cess, and their. account of polar cell-formation, is not, however, 
corroborated, and is vigorously contested, e. g. by Strasburger. 
In the spermatogonia themselves, or in what he calls the sper- 
matoblasts in Astacus, Eriphia, and many other Crustacea, 
Grobben (‘ Arb.,’ Wien, 1878) has described a definite body 
(Nebenkorper) occurring in the protoplasm, sometimes far 
from, sometimes near, or even apparently connected by fine 
filaments with the nucleus, in regard to which he suggests that 
it is, perhaps, a portion of the nucleus of the spermatoblast, 
extruded at maturation, before division into spermatocytes. 
Semper has also described a similar problematic body in the 
corneal mother-cells within which his spermatoblasts are 
formed. A comparison has also been frequently drawn between 
the polar cells and the portions of spermatoblast which seem 
to be excluded from a share in the actual formation of sperma- 
tocytes, e. g. the “ Deckzelle” of Semper, which lies at the 
base of each mother-cell between the spermatoblasts and the 
ampulla wall, in regard to whose origin Semper is undecided, 
