KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 217 
view in his first memoir, where a detailed literary discussion is 
to be found (see ibid., 1876, Sept., and 1877, May). 
The authors of the second and third groups were thus able 
to admit a copulation between the penetrating spermatozoon 
and the complete, or only partially persistent, nucleus. O. 
Hertwig and EH. van Beneden (20) were, however, the first 
to recognise, in 1875, this important fact. 
It must, besides, be here mentioned that the presence and 
copulation of two nuclei (or nuclear-like structures), imme- 
diately after the entrance of the spermatozoon into the egg, 
and before the commencement of segmentation, was clearly 
recognised and maintained by Warneck (201), Biitschli (40), 
and Auerbach (5). Warneck’s observations on Lymneus and 
Limax are somewhat vague: he says that before the segmen- 
tation of the egg two nuclear-like bodies are present, which 
fuse to form a single one, and this, at the beginning of the 
segmentation of the egg, then takes on a biscuit-shaped form. 
Bitschli (‘‘ Beitrage zur Kenntniss der freilebenden Nema- 
toden ’’) also describes the formation of two nuclei in a thread- 
worm (Rhabditis dolichura). These are supposed to arise 
at one pole of the egg close to one another. Biitschli leaves it 
undecided whether one of them (the second) does not arise 
from the other (the first). He found that the two nuclei 
approach one another, and move towards the centre of the 
yolk. The two nuclei have the appearance of fusing com- 
pletely ; yet he thinks that this is not the case, but that the 
appearance is simply due to the nuclei being usually seen 
superposed. Undoubtedly Bitschli does not uphold the fusion 
of the two nuclei in his first memoir on this subject. 
The positive assertion of a fusion immediately after ferti- 
_ lization of two independent nuclei into one, which then sinks 
further into the yolk, is due (after Warneck) undoubtedly to 
Auerbach, who studied Ascaris nigrovenosa and Stron- 
gylusauricularis. Auerbach, whose statements have re- 
ceived much too little consideration,’ reported his observation 
* Thus, for instance, Auerbach stated that the two star figures in nuclear 
division are connected by a middle portion, which he derived, like the stars 
from the nucleus. Vide loc. cit., part 2, Taf, iv, 
