292 M. M. Metcatr 
cases are so doubtful that they can hardly be taken into account 
in endeavoring to understand copulation. They may also have been 
abnormal, division of the body being delayed beyond the proper 
time, giving nuclear relations not found in perfectly normal cells. 
In all other cases described the phenomena were clear. 
It is uncertain what would have been the further history of 
each type of zygote described. When the male nucleus unites with 
one of the nuclei of a binucleated macrogamete, it seems probable 
that the next division would separate the syncarion from the smaller 
nucleus, one going to each of the daughter cells, but I have not 
observed the division of these forms. If the binucleated zygotes do 
divide in this way, one sees no reason why the daughter cell which 
receives the nucleus with four chromosomes might not itself fuse 
with another microgamete to form a uninucleated zygote, just as 
a polar body may be fertilized, but I have made no observations 
bearing upon the point. If it does not do so, it would seem to 
indicate that changed cytoplasmic conditions due to the entrance of 
the microgamete stand as a bar to further copulation. Professor 
Bovert tells me he has never succeeded in fertilizing a nonnucleated 
fragment of an already fertilized sea-urchin egg, though it is easy 
to fertilize fragments of unfertilized eggs. Sufficient study of old 
infections in Opalina would probably determine this interesting 
point. The comparison of these binucleated macrogametes with an 
egg, which has not yet completed its maturation seems a correct 
comparison, for doubtless the typical fully-formed macrogamete in 
Opalina would be uninucleated. Entrance of the male cell in Opalina 
seems to occur either after or during the maturation divisions, as 
in Metazoa. 
The later history is much more doubtful in those cases in which 
the male nucleus divides before fusing with any of the female nuclei 
(cf. Fig. 204 and Fig. 206, Pl. XXIV). Fig. 206 seems to interpret 
Fig. 204 to the extent of showing that the dividing male nucleus 
all goes to one of the daughter cells. Apparently there it must so 
behave as to give four of its eight daughter chromosomes to each 
of the daughters of the female nucleus, but just how this is effected 
we cannot say. It might be either by fusing while the female 
nucleus is still incompletely divided, or by waiting until both nuclei 
are completely divided and then the four daughter nuclei conjugating 
in pairs. I hope to find in the sections of infected recta of the 
tadpoles answers to some of the questions still unsettled, but the 
preparation of the sections is difficult because of the dirt in the 
