772 The American Naturalist. [August, 
The union of the pronuclei is a summation of separate chromatin 
bodies that pass from each nucleus to the equator of a spindle; the 
nuclear membranes disappear and the chromatin breaks up finally into 
V-shaped loops, apparently 12 in each nucleus ; between the nuclei a 
centrosome is seen surrounded by sharp radiating lines, while there are 
also radiations in the protoplasm about the nuclei ; two centrosomes 
are next found at the ends of a small spindle lying between the two sets 
of chromatin loops ; these loops then collect at the equator of the spindle 
that enlarges to form the first cleavage spindle ; these chromatin loops 
are entirely different in size and form from the chromatin bodies seen 
in the formation of the polar body and appear to be not more than 
twenty-four in number. s 
The first cleavage results in the formation of two entirely equal cells. 
The nucleus of each receives some of the above chromatin loops; the 
author supposes they split so that each cell receives 24 chromosomes, 
but this is not evident from his figures and seems rather an inference 
from a general idea supported by his belief that the adult tissues of 
the mouse apparently show 24, and the spermocytes as well as the 
maturing egg 12 chromosomes. 
The subsequent cleavage taking place as the egg passes toward the 
uterus is at first unequal in that one of the cells enlarges and divides 
into two; there are then three cells, one large, a pair of smaller. The 
larger then divides into two smaller than the first formed pair. The 
first formed then divide so that there are now six ; then the others 
divide and the egg is made up of eight all essentially alike. The egg 
has 16 cells about 72 hours and comes into the uterus about 80 hours 
after coitus. 
If the eggs are not fertilized, either from the lack of copulation or 
from the fact that not enough sperm enters the oviduct to fertilize all 
the eggs, they degenerate without cleaving. 
Interesting cases of polyspermy were seen to result from a second 
copulation ; if when the vaginal plug is fallen out a’ second male be ad- 
mitted, the usual changes in the uterus take place. In one case when 
the second copulation occurred 18 hours after the first, a sperm was 
found in an egg having two normal pronuclei, and in another a small 
pronucleus in addition to the two normal ones. In another case of 
copulation 24 to 36 hours after the first, where the eggs had divided 
into two cells, two sperms were found in one cell of one egg and a 
large nucleus (apparently a male pronucleus) in a cell of another egg, 
in addition to the normal nucleus of the cell. 
