384 :N'aoliidc Yatsu. 



Coe ill the egg of C. marginatus at the anaphase of the iirst cleavage 

 mitosis ('99, Fig. 31) is seldom met with in that of C. lacieus. 

 It, however, occnrs so seldom that it would be more natural to look 

 upon this figure as the result of fixation or some other abnormal 

 conditions. Spiral asters are also seen at the poles of the maturation 

 spindle, but their occurrence is so inconstant that the figure should 

 be interpreted as due to some accidental disturbance rather than to 

 any constant cause. 



V. Cytodiebksis. 



{a) Ohserralioiis. 



In the hope of finding some key to the solution of the mechanism 

 of cell division, the first and second cleavages of the egg of C. lacteus 

 have been studied. For the sake of convenience the results will be 

 described under five headings : 



1. Movemoit of Chromosomes and Centres. 



In order to determine the relative movement of the chromosomes 

 and the centres, I have measured sections of twenty-five eggs at 

 the metaphase and at the mid-anaphase."' 



Metaphase — 46.73 microns from the equatorial plate to the 

 periphery (through the center). 

 16.415 microns from the equatorial plate to the 

 centriole. 

 Midanaphase — 46.00 microns from the middle plane of the spindle 

 to the periphery (through the center). 

 19.09 microns from the middle plane of the spindle 



to the centriole. 

 10.78 microns from the middle point of tlu; chromo- 

 somes to the centriole. 

 The movement of the chromosomes is 8,310 microns. 

 The movement of the centriole is 2.675 microns. 



''"Only vertical seftinns wore made use of in which the plane passed the t.vo 

 opposite centrioles. 



