612 
T. H. MORGAN 
The eggs while still enclosed in the ovary show the polar spindle ; 
and in some cases I have found sperm nuclei in the eggs, showing 
that if sperm are in the water they may penetrate to the ovary 
and fertilize the egg there. But fertilization is not essential to 
the ripening of the egg, as shown in cases where the eggs are laid 
in the absence of the male. 
The effect of centrifuging the ovarian egg is shown in plate 4,. 
figs. 1-6. When the germinal vesicle is intact it is carried to one 
side of the cell; above it an oil cap forms, but the cap is less appar- 
ent than in eggs that have been laid, and also less concentrated, 
figs. 1 and 2. It is in fact sometimes difficult to detect the oil cap 
in the ovarian eggs. The yolk also appears less easily moved. 
At first I was inclined to interpret this as due to the more fluid 
parts of the egg being still retained in the nucleus, but the same 
conditions, although less pronounced, are present in ovarian eggs 
in which the germinal vesicle has been dissolved, figs. 3-5. It 
appears, therefore, that the egg must absorb water after it is laid, 
and becomes, in consequence, less viscid: so that its lighter and 
heavier substances are more easily separated. 
General consideraiions 
Four points of interest are particularly well illustrated by the 
action of a centrifugal force on the egg of Cumingia. 
First : The question of the role of the visible substances of the 
egg as organ-forming materials; 
Second: The formation of the aster and its relation to the chro- 
mosomes; 
Third: The movements of the aster in the egg; 
Fourth: The bearing of the results on the phenomenon of 
cleavage. 
These points ma}- now be discussed in turn, and although the 
last three are more closely related to each other than to the first, 
yet their correct interpretation has an important bearing on the 
first question. 
The role of the visible substances in the egg as organ-forming 
materials. The results with the egg of Cumingia, an egg that shows 
