620 
T. H. MORGAN 
appearance in the preserved egg. A broad cap corresponding to 
the oil cap of other eggs is found between the surface of the eggs and 
the outermost wall of the displaced nucleus. Since the material is 
not dissolved out in the alcohol, xylol or acids, it is probably not 
oily. Within it however a few vacuoles may often be found which 
probably are the holes left by dissolved oil. The scattered gran- 
ules, mentioned above, that stain with basic dyes, are also pre- 
sent and are driven with the yolk to the outer pole. They form 
the dark cap sometimes present on the yolk sphere. The forma- 
tion of the yolk ring is difficult to explain. I have not found it 
conspicuous in the eggs obtained at Harpswell. Differences in 
the rate of centrifuging in the two cases are no doubt responsible 
for the results. The New Haven eggs were probably rotated 
m.ore slowly; but the difference between the two sets cannot be 
entirely explained by the time of centrifuging but perhaps by the 
preservatives, since Harpsw^ell eggs, rotated only fifty times, show 
no evidence of rings although the yolk has begun to move to 
one pole. 
The relation between the yolk ring and the nucleus is interesting. 
As the ring moves from the periphery of the egg towards the cen- 
ter of the egg it encloses in its polar portion the germinal vesicle. 
A later stage shows the nucleus passing through the ring as the 
nucleus moves to the pole and the ring towards the antipole. 
Obviously the material of the ring is made up of the yolk gran- 
ules situated near the surface of the egg, but this does not explain 
whj^the yolk granules move inwards towards the center of the egg; 
rather should we expect them to move by the most direct path 
to the antipole, unless the interior of the egg is more fluid and 
therefore less resistant to the yolk granules than the more cortical 
layers. Lillie explains the similar ring formation seen in Chaetop- 
terus in this way, and I incline to adopt his suggestion. The yolk 
spheres move with low centrifuging in an oblique course outwards, 
in consequence of the centrifugal force, but somewhat towards 
the center of the egg because the resistance is less here than in 
the cortical layer. When a high rate of centrifuging is employed 
the yolk granules respond more directly to the centrifugal force. 
