CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 595 
When collected, the animals were generally put into a tumbler 
and brought in dry. It appears that a short removal from the sea- 
water excites them to egg laying, but the same process will also 
occur if the animals are brought in with the mud in which they 
live. The males shed their sperm first. The females lay their 
eggs even when no sperm is present. It seems that the presence 
of sperm in the water may incite the females more promptly to 
deposit their eggs though the presence of the sperm is not necessary. 
The eggs are small and very numerous if the female is large, and 
if she has not previously spawned. Early in June fewer individuals 
lay eggs, and the eggs produce fewer normal embryos. Later in 
June and especially in July the egg-laying season is at its height, 
while in August fewer eggs are again obtainable. It is notice- 
able that these late eggs show signs of parthenogenesis. The polar 
bodies are extruded and an irregular cleavage often takes place. 
I have already published two preliminary notes touching on 
some points concerning the centrifuged egg of Cumingia, but man}' 
of the results appear here for the first time. 
The effect of centrifuging on development 
WTien the egg is laid (plate 1, fig. A) the polar spindle is pres- 
ent in its middle (plate 2, fig. M). If sperm has been added to 
the water, before egg laying begins most of the eggs will have been 
entered by one (or more) sperm. After centrifuging the egg has 
the appearance seen in plate 1, fig. B; plate 2, fig. N. The oil 
is driven to one pole, and the heavier pigment and yolk to the 
other. The broad middle region is occupied by the clear proto- 
plasm. The details of the polar-body formation and cleavage 
will be given later. Here I need only say that during these proc- 
esses the enforced distribution of the materials may become 
altered, not in consequence, as is sometimes implied, of the remix- 
ing of the materials of themselves, or returning to their original 
position, but because of the movements of the karj'^okinetic 
spindle, and because of the process of cell division, plate 1, fig.F. 
Despite these changes the centrifuged materials often remain in 
large part segregated at the time of division, and, in consequence, 
