STUDIES WITH THE CENTRIFUGE 27 



Cyclops, where he believes it persists to a very late stage in devel- 

 opment. That it persists in the spindles is shown by the frequent 

 separation of the two parts of the spindle during centrifuging 

 (fig. 3). The asters at the poles of this double nucleus consist 

 of masses of protoplasm, indistinguishable from that which sep- 

 arates the yolk spheres. There is no visible centrosome or appear- 

 ance of astral fibers in the protoplasmic mass. The only radial 

 appearance is afforded by the yolk spheres, which radiate from 

 this center in rather regular rows, and by a few paths of proto- 

 plasm, broader than the rest, passing out from the central mass 

 between the rows of yolk spheres (fig. 7). 



The earlier nuclear changes of living eggs are readily followed 

 with the lower powers of the compound microscope. Eggs which 

 have just been deposited in the sacs have a light gray spot near 

 their periphery; this is the second polar spindle. Since there is 

 no definite relation between the position of the spot and the axis 

 of the egg sac, it is probable that the eggs are not oriented in the 

 sac. At the end of half an hour the second polar body has been 

 given off, the nucleus has moved to the center of the cell, is much 

 enlarged and is a distinct gray disc. Later it seems to fade out 

 a little, gradually elongates in the long diameter of the cell, and 

 the outline of spindle and asters can be seen. With the oil immer- 

 sion lens the rows of yolk spheres, radiating from the gray center 

 of the aster, may also be seen. 



The first cleavage plane appears an hour after the egg sacs / 

 have formed. The daughter nuclei round off into gray discs in/ 

 the center of the blue-gray cells, and in ten to fifteen minutes 

 begin to elongate in a direction parallel to the first cleavage plane. 

 The second cleavage follows in half an hour after the first, and the 

 third cleavage is complete at the end of the second hour. The 

 egg then consists of eight equal cells. Beyond this point the cleav- 

 ages have not been traced. The eggs are crowded together in the 

 sac so closely that most of them are flattened in one diameter. 

 Indeed, the egg at the open end of the sac is the only one which 

 is spherical. I examined between fifty and sixty normal eggs and 

 found the cleavage plane regularly cutting through the shortest, 

 diameter of the cell. McClendon has found that in certain para- 



