46 CARL G. HARTMAN 
matter is again mentioned and the photograph presented as 
further evidence that there is a decided difference between the 
normal 4-celled egg in the opossum and that of Dasyurus. What 
has been described by various authors as ‘parthenogenetic 
cleavage’ in ovarian eggs of mammals may often be merely a 
fragmentation process similar to that here described for the 
opossum. I have also found just such fragmenting eggs in 
atretic follicles of opossum ovaries. 
h. Deutoplasmolysis or the elimination of yolk 
In the eggs of both Dasyurus and the opossum the extrusion 
of yolk proceeds in the manner that one might predict from the 
distribution of the yolk in either case. In the ripe egg of 
Dasyurus the deutoplasm is collected in a mass at one pole 
where it is bodily extruded when the first two blastomeres round 
up during the first cleavage. In the opossum the yolk, being 
peripherally distributed, is given off from any or all sides. This 
happens, in small amounts, as early as the pronuclear stage and 
in larger amounts at the first cleavage. At each cleavage stage 
some yolk is left within the blastomeres, and it is probable that 
with each succeeding division of the blastomeres some additional 
yolk masses are eliminated. There seems to be no regularity of 
time in the elimination of the yolk, just as there is no regularity 
in the relative amounts eliminated; but the greatest quantity 
seems to be given off between the 2- and the 4-celled stage. 
The blastomeres may be very large, and full of yolk or very 
small and proportionally yolk-free; and, since considerable cyto- 
plasm is thrown off with the yolk, this would seem to indicate 
that a relatively unimportant role is played by the peripheral 
cytoplasm in the normal processes of the cells. But the fate of 
the yolk is in all cases the same: it is eventually digested and 
resorbed, so that in the bilaminar stage only a few granules 
occur among the cells of the embryonic area, as will be pointed 
out later. 
As the eliminated material contains both cytoplasm and yolk 
granules, it would seem that whole portions of the cells are 
