CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 613 
all the characteristic features of precocious development, tally 
completely with the results on the frog and sea-urchin. The 
visible substances of the egg that can be centrifuged are not organ- 
forming. Centrifuging may, it is true, cause abnormalities in 
the development in more than one way, but such abnormalities 
can generally now be referred to the real cause and that cause is 
not the segregation of the visible materials of the egg. It has 
been well worth the time and trouble that it has cost to work 
out these other causes of abnormalities; for, there has been a 
tendency on the part of some embryologists to attribute all abnor- 
mal development after centrifuging to the lack of redistribution of 
the visible materials. The repeated failures in the case of Cumin- 
gia to get normal embryos after centrifuging well illustrate this 
point. By a fortunate circumstance the small size of the animal 
made it possible to centrifuge the eggs within the animal and to 
have these eggs laid normally, when normal development was the 
rule. 
Some other causes of abnormal development may be briefly 
referred to. In eggs with a large amount of yolk its transporta- 
tion to one part of the egg may interfere with normal develop- 
ment, because of the mechanical difficulty of nucleohzation of 
this part of the egg, or because of difficulties in the movements of 
yolk-laden cells during gastrulation. The compactness of the yolk- 
mass may likewise interfere with the orderly sequence of the cleav- 
age, etc. In eggs kept in the centrifuge for a long time the resting 
nuclei may be carried so far away from the spindle that their 
chromatin may fail to reach the spindle, or else reaches it in such 
a form that an irregular distribution of the chromatin takes place 
with injurious after-effects. Even in an egg as small as that of 
Cumingia such effects are visible. 
Handling the eggs may affect them in various ways, as is 
excellently shown in the present case. The sojourn of the eggs in a 
confined space may also seriously affect them, if kept there for a 
long time. 
These and many other factors may induce abnormal develop- 
ment. Despite these possibilities the results show plainly that 
normal development may follow when the visible substances 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 3. 
