994 W. WALDEYER. 
Invertebrates, too, Selenka (1. c.) and Schneider (1. ¢.) have observed super- 
fertilized eggs to develop normally. 
On a third essential point, namely, the fusion, we have 
not yet come to a final conclusion. Certainly this ‘‘ conjuga- 
tion,” or “ fusion,” of the two nuclei, or “ pronuclei,” as we 
may now call them, offers no small difficulty. 
The first observers, Warneck and Auerbach, who maintained 
a fusion, have interpreted the relation chiefly in the sense of 
the word “ fuse.” Auerbach held that the fused nuclei lose 
themselves in the protoplasm of the cell (karyolysis). Such an 
idea was natural, so long as nothing was known of the process 
of karyokinesis, and the thread-like structure in all nuclei was 
unknown. How does this bear on the question of fusion ? 
I have already stated that in every nucleus, besides the 
easily-staining, so-called chromatic substance (“ chromatin” of 
Flemming), there are to be distinguished the nuclear mem- 
brane and the so-called “ achromatin,”? which is identical 
with “nucleoplasm.” I also mentioned that Balbiani and 
Pfitzner have shown that the chromatic threads are made up 
of small, nearly equal portions, the so-called “ Mikrosomes,” 
and that in nuclear division two more structures make their 
appearance, the “ polar bodies”’ (Polkérperchen), and a second 
thread-structure arranged as a spindle, the so-called “ nuclear 
spindle,” or “spindle figure,” together with the “ attraction- 
sphere.’ The threads of the spindle figure differ from the 
chromatin threads in their less capacity for taking stains, in 
their fineness, and in their characteristic arrangement. 
When at the present day we speak of a “fusion,” “ copula- 
tion,” “ conjugation ”—or whatever we may call it—of nuclei, 
it is necessary to examine the relation to that process of the 
several constituents of the nuclei just mentioned in order to 
have a clear conception of it. In other words, we must try to 
ascertain how the nucleoplasm, the achromatic spindle, &c., are 
related to one another during the fusion of the chromatic 
threads, and must also take into consideration the microsomes. 
Boveri, in his recent contribution (34), speaks to the same 
effect. As for the sperm-nucleus the question is so far simpli- 
