90 CARL G. HARTMAN 
half of the ten-day period of gestation. More exact figures 
have not as yet been worked out. 
8. The first polar body is given off in the ovary, the second 
in the Fallopian tube as in other mammals (pl. 14). 
9. In the Fallopian tube much albumen and the shell mem- 
brane are added to the ovum. It probably requires about 
twenty-four hours for the passage of the egg to the uterus. 
10. The haploid number of chromosomes in the opossum is 
twelve (pl. 14). 
11. At no stage in the unsegmented egg is there any evidence 
of polarity in the distribution of the yolk, as in Dasyurus, the 
bat and some other mammalian eggs, although in the opossum 
the yolk is abundantly present (pls. 13 and 14). 
12. The egg varies considerably in size, but on the average it 
is about 0.12 mm. in diameter through the ovum and 0.6 mm. 
through the shell membrane. Some normal eggs attain the 
diameter of 0.73 mm., owing to the larger amount of albumen 
deposited (compare fig. 2, pl. 4, and fig. 3, pl. 5). 
13. As in probably all marsupials, the egg reaches the uterus 
unsegmented, hence at an earlier stage than in any of the 
Eutheria. 
14. The pronuclei at first occupy a yolk-free area at the 
periphery of the egg; then migrate to, the yolk-free central 
portion, where the first cleavage spindle is later to be seen 
(figs. 20 and 21, pl. 14). 
15. Deutoplasmolysis or elimination of yolk begins at the 
pronuclear stage, continues at the 2-celled stage, and reaches 
its maximum during the second cleavage (pls. 3 and 15). 
16. The quantity of yolk and surrounding cytoplasm extruded 
varies greatly, hence the size of the blastomeres varies in inverse 
ratio to the extent of deutoplasmolysis (pl. 15). 
17. Deutoplasmolysis occurs by elimination of masses of 
various sizes on all sides of the egg, not at any particular spot 
or pole, as in Dasyurus and the bat (fig. 4, pl. 3). 
18. The two blastomeres of the 2-celled stage are usually of 
the same size, shape and‘structure, or they may differ in size. 
This difference is probably due chiefly to the difference in the 
amount of yolk extruded (text fig. 4). 
