232 W. WALDEYER. 
Flemming (5%) clearly distinguished between the different 
substances of the copulating nuclei, and described the process 
in detail. According to him, the chromatin of the male pro- 
nucleus would be handed over to the female pronucleus, and 
consequently the store of chromatin in the latter would be 
increased. He also observed the clear substance which sur- 
rounds the chromatin of the male pronucleus like a halo, and 
can be recognised at the very moment of the copulation ; yet 
he did not succeed in coming to a clear view as to the final 
result. Schneider (181) who was the first, since H. Munk 
(143), to use and recommend the thread-worm of the horse for 
embryological research, arrived at the conclusion, for this and 
other animals, that no fusion between a male pronucleus 
derived from the spermatozoon and the female pronucleus is 
established, but that the spermatozoon disappears in the yolk 
“like a cloud.’ He therefore reverts to the old opinions. 
Eberth and Nussbaum then undertook a testing of Schneider’s 
statements making use of Echinoderms and Worms. So far 
as I am aware, only a short account has been up till now 
published by Eberth (56), who upholds the fusion, in opposi- 
tion to Schneider, but gives nothing new as to its nature. 
Eberth observed in Echinids (Spatangus), that during the 
contact of the egg-nucleus and sperm-nucleus the fine parti- 
tion wall between them disappears, and that then the two fuse. 
In this way a “ mixing of the chromatin and achromatin ” of 
the two nuclei is brought about. The egg-nucleus has 
obtained an increase of chromatin, and probably also of 
prochromatin (see Part I), since in the segmentation nucleus 
a much larger quantity of chromatic granules and threads can 
be observed. 
Nussbaum published his first memoir (149) in August, 1883. 
He describes the extrusion of the two directive corpuscles and 
the transformation of the remains of the germinal vesicle into 
a structure having the form of a resting nucleus; likewise the 
transformation of the intruding spermatozoon-head into asecond 
nucleus of a so-called “ resting form.” He further positively 
asserts the fusion of these two nuclear structures, although 
