170 Schrader. 
As already intimated, union of the pronuclei restores the diploid 
number. The first cleavage, as well as succeeding divisions in the 
egg, are perfectly normal and ten chromosomes are distributed to each 
pole at every division. 
Polyspermy does not seem to be of common occurence, for in only 
two out of more than sixty cases was an extra sperm nucleus observed 
in the egg. In both cases five chromosomes had been evolved, but the 
presence of several normal cleavage nuclei indicated that a union of 
pronuclei had taken place some time previously. Since no traces of 
supernumerary sperms were found in later stages, I assume that such 
nuclei do not take any part in the further development. 
The Polar Bodies. 
At the time when the female pronucleus goes to the center of 
the egg, two polar bodies are left at the periphery. The first polar 
body, which remained inactive after the first maturation division, still 
retains the huddled and irregular arrangement of its five dyads. In 
some cases however, the components of each dyad remain closely together, 
whereas in others even this collocation is lost. In the succeeding 
phase, the unit elements of all five dyads become scattered, and a 
nuclear wall is formed around them (Fig. 10a). Finally the chromosomal 
elements become diffuse and the nucleus enters the resting condition. 
It is barely possible that the first polar. body may actually divide on 
occasion, but this must be an exceptional condition for only one very 
doubtful case was encountered. From the preceding account it will be 
seen that in normal cases there are now two polar bodies at the peri- 
phery; the chromatin elements or chromosomes of the first polar body 
are ten in number, while the second contains five. 
Even before the first polar body has entered the resting con- 
dition, it, as well as the second polar body, begins to expand. 
Separated from each other up to this time, the two simultaneously 
begin to approach until they come in contact (Fig. 12). In the following 
stage only one nucleus is present, which is distinctly larger than either 
of the bodies just mentioned and is without doubt the result of their 
fusion. This nucleus, which may be called the polar nucleus, now 
undergoes the usual phases in the formation of chromosomes (Fig. 13). 
As might be expected, the number of chromosomes evolved is fifteen 
(Fig. 14 and 15). The division following their arrangement in the 
metaphase plate, seems to be normal in every way, and fifteen chro- 
