424 FRANK R. LILLIE 
disappears (figs. 14a, 146 and 15). There can be not the least 
doubt of this fact in my material, though Bonnevie, working on 
the same form, but with different cytological methods, remains 
doubtful on this point. I shall not attempt an elaborate cytologi- 
cal analysis of the matter here (though the evidence from this 
side is, I believe, conclusive), because in eggs from which the 
sperm nucleus has been removed experimentally the gradual 
disappearance of the egg aster can be traced with complete cer- 
tainty, owing to the absence of any possible confusion with the 
sperm aster (see second part of this paper, p. 440). The fulty 
formed egg nucleus in such: eggs never has a trace of the aster 
(see studies 2 and 4). The chromosomes of the egg swell and 
form vesicles (figs. 14 a, 14 6, 15), which gradually fuse together 
and establish the egg nucleus. At the same time the sperm 
nucleus begins to enlarge (fig. 14 6) and the sperm amphiaster 
becomes less distinct than before and its radiations less extensive 
(figs. 138, 14 and 15). The sperm amphiaster continues to wane 
and when the two germ nuclei have come together, the smaller 
aster has become indistinguishable (fig. 15). The larger aster 
can, however, always be distinguished through the stages of the 
germ nuclei, and can be seen to become the larger aster of the 
first cleavage spindle after the partition wall between the germ 
nuclei has disappeared (figs. 16 a, 16 6, 17). At this time a 
much smaller aster arises opposite the larger (fig. 17), like it in 
the plane of apposition of the germ nuclei. The first cleavage 
spindle is thus heterodynamic from its inception, and the first 
cleavage of the egg is strikingly unequal, as is well known from 
Wilson’s study (Wilson, 794). 
In the preceding paragraph I have summarized a very compli- 
cated period of the fertilization process to which I have given 
much study, and which exhibits many interesting cytological 
details, as for instance, the accumulation of granules in the neigh- 
borhood of the germ nuclei (figs. 15 and 16 a) which almost 
certainly escape from the latter (fig. 16 a). As regards the 
main point, the origin of the cleavage centers, there can be no 
doubt that the larger one is derived from the larger aster of the 
sperm amphiaster, for it can be followed continuously and is 
