240 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
the egg permanently and which saves it from the disintegra- 
tion which follows membrane formation. 
3. In the preceding experiment blastomeres were fertilized 
which had ceased to segment for about twenty hours. The 
experiment leads, however, to an entirely different result if 
sperm is added while the blastomeres are in active partheno- 
genetic cell division. If we add sperm to such eggs (S. purpura- 
tus), they form a fertilization membrane, but they do not 
develop very far. The entrance of a spermatozoon into the 
blastomere of an egg which is in active parthenogenetic seg- 
mentation leads to the rapid disintegration of the egg or blas- 
tomere; while the entrance of a spermatozoon into a partheno- 
genetic blastomere which has gone back into the resting stage 
for some time, can cause the development of the blastomere 
into anormal pluteus. What causes this difference? Possibly 
the fact that the blastomere which had gone back into the rest- 
ing stage for some time has lost centrosomes and astrospheres, 
while the egg which is in active parthenogenetic cell division 
possesses both organs. 
These blastomeres in which fertilization by sperm is super- 
imposed upon artificial parthenogenesis while the eggs are 
still in active development behave like eggs fertilized by more 
than one spermatozoon. *Driesch found that eggs which had 
been fertilized by more than one spermatozoon do not, for the 
most part, develop beyond the blastula stage.1 Boveri has 
explained this by the fact that such an egg possesses more 
than two astrospheres.2 As we know, the division of the 
nucleus into two daughter nuclei depends upon the fact that 
the dividing egg forms two astrospheres. This is the case 
not only in fertilization by sperm, but also in the development 
started by the methods of artificial parthenogenesis. But 
1 Driesch, ‘‘Ueber die Furchung doppelbefruchteter LEier,’”’ Zeitschr. /. 
wissenschft. Zool., LV, 1892 
2 Boveri, Zellenstudien, Heft 6; Die Entwicklung dispermer Seeigeleier, Leipzig, 
1907. 
