258 W. WALDEYER. 
sperm-cell undergoes till the final product, the spermatozoon, 
are attained. Biitschli thinks that he can find in the extrusion 
of the directive corpuscle from the egg-cell an analogy with 
the behaviour of the equivalent primary sperm-cell. 
Biitschli’s theory would fall to pieces if it be established 
that sperm mother-cells also give rise to directive corpuscles. 
This is a postulate whether we believe in the bisexuality of 
cells with E. van Beneden (not Minot), or in Weismann’s 
theory. I have already mentioned that E. van Beneden has 
described in Ascaris megalocephala certain facts which 
can be explained in the simplest way as an extrusion of direc- 
tive corpuscles during sperm-formation. If, then, these bodies, 
originally scarcely heeded, should turn out to be perhaps of 
great importance, we might adopt E. van Beneden’s view, or 
acknowledge that of Weismann. ‘To the difficulties which 
oppose van Beneden’s explanation I have already alluded. 
Whether Weismann’s hypothesis will, after further researches, 
turn out to be tenable remains to be seen. It may be added 
that the assumption of two modifications of Kernplasma—viz. a 
‘“‘Keimplasma” and a “‘histogenic Kernplasma”’—has acquired 
substantial support through A. Gruber’s observations on the 
conjugation of Paramecium aurelia (81). In thisanimal a 
chief nucleus and a paranucleus can be distinguished ; only the 
latter is concerned in conjugation. During and after conjugation 
eight young nuclei arise from the paranucleus ; the nucleus 
divides up into numerous small pieces. Four of the products 
of the paranucleus unite to form a new paranucleus ; the four 
others unite with the fragments of the old nucleus, and thus 
form the new nucleus. Gruber’s idea that the paranucleus 
contains essentially the Keimplasma, and the nucleus histo- 
genic Kernplasma seems to be well founded. 
Boveri’s (35) highly important observation recently pub- 
lished must also be mentioned here, viz. that in the repeated 
divisions of the egg of Ascaris megalocephala a difference 
in the structure of the nucleus is soon shown. The two first seg- 
mentation-spheres are readily distinguishable from one another 
as soon as they prepare for further division, One sphere (a) 
