650 
T. H. MORGAN 
Is gravity a factor in the formation of the hlastodiscf 
The blastodisc appears on that part of the normal egg that is 
turned down or outwards on the centrifuge. The normal orien- 
tation of the egg, as it floats in the sea, is due to gravity. Does 
gravity acting in the same way as does the centrifuge besides 
orienting the egg also produce the blastodisc? 
I tested this possibility by placing the eggs in a long test tube 
half-filled with water. A bicycle was turned upside down and a 
jet of water from a faucet allowed to run over the outer edge of 
the tire of one wheel, which caused the wheel to turn 10 revolutions 
per minute. At each revolution the water and eggs fell twice from 
one end of the tube to the other so that the eggs were kept con- 
tinually whirling irregularly in the tubes and were practically 
never at rest. The eggs were fertilized at once and placed on the 
wheel. The eggs were kept on the wheel until the two and four 
cell stage appeared. They were then removed and developed 
normally. 
The blastodisc of the rotated eggs resembled the normal one in 
every respect. Evidently gravity is not necessary for the for- 
mation of the blastodisc even although the direction of its action 
is the same as the direction of the centrifugal force of the machine. 
In the light of the discussion between Moszkowski on the one 
side, and of Katheriner and myself on the other, concerning the 
role of gravity in the development of the frog's egg, it is not with- 
out interest to note that these rotated fish eggs developed in a 
perfectly normal way. Moszkowski claimed that the action of 
gravity is essential for the normal development of the frog's 
egg. This was denied by Katheriner and myself on the basis of 
experiments carried out to test the question. The results on the 
fish show that in this egg also the action of gravity in a constant 
direction is of no importance for normal development. 
Abnormal embryos after centrifuging 
- Since the centrifuge causes no stratification of the materials of 
the egg of the fish (except in so far as it facilitates the formation of 
