218 W. WALDEYER. 
in 1874, before the Breslauer Naturforscher-Versammlung, 
and published them in the same year. 
Later (1875), Biitschli (41, 42) also observed the process of 
fusion in various nematodes and molluscs ; he extended existing 
knowledge herein that in certain species of animals he saw 
from three to five nuclei make their appearance at the surface 
of the yolk, and then fuse at the centre of the egg. 
However, none of the hitherto mentioned observers recog- 
nised that one (or more) of these nuclei arise from the 
spermatozoa and the other from the germinal vesicle. As a 
precursor of this view, it was indeed suggested by Biitschli 
tentatively, that a portion of the substance of the spermatozoa 
might take a share in the formation of the nuclei in question. 
O. Hertwig (93) deserves the credit for one of the first 
definite declarations on this fundamental point. E. van 
Beneden (20, 21) too, had at the same time and independently 
of Hertwig, written to this effect, but his view does not point 
to a morphological continuity between the spermatozoon and 
one of the copulating nuclei. 
O. Hertwig, in his first memoir, describes the process of 
maturation and fertilization as occurring in such a way that 
the germinal vesicle is carried towards the surface of 
the yolk by contraction of the egg-protoplasm. Its mem- 
brane disappears, the contents fall to pieces, and become 
absorbed by the yolk; the germinal spot seems to remain 
unchanged and to become the permanent nucleus of the egg, 
which is now capable of fertilization. O. Hertwig agrees also 
with the above-mentioned view of Derbés, &c. He calls this 
reduced nucleus, arising, according to his opinion at the time, 
from the germinal spot, the “ Eikern” (egg-nucleus) ; whilst 
to the previous nucleus he would give the old name “ Keim- 
blischen ” (germinal vesicle). 
The second nucleus, which Bitschli and Auerbach had 
already seen, and the copulation of which, with the first 
nucleus, they had described, is now recognised by O. Hertwig 
as the head of the penetrating spermatozoon—and 
herein lies his greatest merit. He comes to this conclusion 
