126 David Day Whitney 



The following experiments and observations were made at 

 the suggestion and under the supervision of Prof. T. H. Mor- 

 gan. 



II RELATION OF THE FIRST CLEAVAGE PLANE TO THE STRATIFI- 

 CATION OF THE MATERIAL OF EGGS CENTRIFUGED WHEN THE 

 GERMINAL VESICLE IS INTACT 



If several hundred animals are centrifuged at the same time 

 and are examined immediately many can be seen to contain eggs, 

 the contents of which are sharply differentiated into three zones. 

 As the animals are thrown down during the centrifuging process 

 in any position the stratification of the eggs may lie in any relation 

 to the median longitudinal axis of the female. The pink zone 

 may be toward the head or foot of the animal, toward the side 

 next the stomach or on the opposite side, or in any other inter- 

 mediate position. The gray zone is always on the opposite side 

 of the egg from the pink zone and the middle zone between the 

 two. The germinal vesicle is found at the junction of the clear 

 middle and pink zones and can be easily recognized owing to its 

 large size (Fig. i). 



From the various lots of females, centrifuged twenty thousand 

 revolutions, eight were selected containing the pink zone toward 

 the head of the animal and the gray zone toward the foot. The 

 germinal vesicle was plainly visible near the line between the clear 

 middle and pink zones. 



Each of these eggs was carefully watched while it remained in 

 the oviduct of the female as well as after it was laid. In every 

 egg the first cleavage appeared at that end of the egg which con- 

 tained the pink pigment. The first division was unequal as it is 

 in the normal egg. In some cases all the pink zone was cut off 

 in the smaller cell while in other cases only a part of it was included 

 in this cell. The gray zone was always included in the larger 

 cell. 



Six other females which had the pink zone of the egg toward 

 the foot of the animal and the gray zone toward the head were 

 isolated and the further history of each egg was carefully followed. 



