444 
EDWIN G. CONKLIN 
symmetry cannot be inverted by these methods. The evidence 
seems to me more than ever conclusive that inverse symmetry 
is associated with inverse polarity, but polarity is evidently a 
more fixed and fundamental property than I had formerly sup- 
posed. 
5. It is very evident that the injurious effects of centrifuging 
increase rapidly from the time of the first maturation to that of 
the first cleavage. Before the formation of the first polar body the 
eggs stand contrifuging without much injury. After both polar 
bodies have been formed and up to the period of the first cleavage 
the effects of centrifuging are more and more injurious. Experi- 
ments 1-0 and 10-12 show that when eggs are centrifuged for 
about 10 min. in the germinal vesicle stage they generally develop 
normally; when centrifuged for a like time during the formation 
of the first and second polar bodies, about half of the eggs develop 
normally, while the other half become abnormal (Exps. 6, 7, 14) ; 
when centrifuged after both polar bodies are formed a much 
larger number develop abnormally until, in the case of eggs centri- 
fuged at the time of the first cleavage, every egg becomes abnor- 
mal (Exps. 7-9 and 15-22). It is, evident that these injurious 
effects are not due to mere separation of ooplasmic substance, 
nor to the axis of such separation, for the effects of centrifuging 
are least injurious precisely at the time when the substances can 
be separated most completely and in any axis of the egg. It is 
also evident that the injurious effects of centrifuging are not due 
primarily to injuries to the mitotic figure, since these injuries 
are not limited to eggs centrifuged during periods of mitosis. 
Eggs centrifuged during the maturation divisions usually develop 
normally, those centrifuged in the resting stage before the first 
cleavage rarely do. The injurious effects of centrifuging increase 
gradually from the period of the first maturation to that of the 
first cleavage irrespective of whether the eggs are centrifuged 
when in division or in rest. 
It seems probable that this increase in the injurious effects of 
centrifuging as the egg approaches the first cleavage stage is due 
to (a) increasing differentiation of the egg, and (b) decreasing 
opportunities for readjustment of displaced substances. In all 
