946 W. WALDEYER. 
matin threads in van Beneden’s sense does not agree with the 
conditions observed by them. They found that when a sper- 
matozoon penetrates into a non-nucleated but still living 
portion of egg-protoplasm, the former can be converted into 
a thread-spindle. Again, when the zoosperm and the egg- 
nucleus do not meet, they acquire the power of becoming 
karyokinetically differentiated directly they are merely lodged 
in the egg-protoplasm. The Hertwigs therefore conclude 
that the plasma of the egg-cell, as well as the substance of 
the spermatozoon, must be endowed with peculiar powers, 
which act upon one another when both portions come into 
contact. Again, Kolliker (108) contributes various doubts, 
which have their origin in the fact that some of van Beneden’s 
figures themselves point to a fusion, and that the separa- 
tion of male and female nuclear substance in the daughter- 
cells formed after the first has not yet been proved. A. 
Schneider’s important memoir (180) also advocates fusion. In 
the conjugation of Anoplophrya circulans (an Infusorian) 
the two nuclei appear as two transversely placed parallel strings, 
which pass from the middle of one individual to that of the other. 
After conjugation each of the two individuals contains two half- 
nuclei, that is, one half of its own previous nucleus, and a half 
of that of its fellow. The two half-nuclei must now completely 
fuse to form one new nucleus. Schneider’s account of the 
nucleoli! is peculiar. Each of the copulating individuals con- 
tains four of them. Whether these are also exchanged he leaves 
undetermined. On the other hand three nucleoli disappear, 
for after copulation only one remains. Have we perhaps here 
to do with directive corpuscles ? | 
I must point out that the adherents of ‘‘fusion” have 
hitherto given us no clear notion as to what is to be under- 
stood by it. Again, the expression “ Durchdringung ” used 
by the brothers Hertwig does not help to explain matters. 
By all observers we find it recorded that the chromatophilous 
male and female elements divide inte “ microsomes ”—in the 
Balbiani-Pfitzner sense. Those who support a ‘ fusion” can, 
' © Paranuclei”’ or “ micronuclei,” Tr. 
