THE DIVISION OF NUCLEI. 201 



of the base of the double cone the filaments present knots 

 or thickenings, just as if they were so many threads with 

 a bead in the middle of each. When the nuclear spindle 

 is viewed sideways, these beads or thickenings give rise 

 to the appearance of a disk traversing the centre of the 

 spindle. Soon each bead separates into two, and these 

 move away from One another, but remain connected by a 

 fine filament. Thus the structure which had the form of 

 a double cone, with a disk in the middle, assumes that of 

 a short cylinder, with a disk and a cone at each end. But 

 as the distance between the two disks increases, the 

 uniting filaments lose their parallelism, converge in the 

 middle, and finally separate, so that two separate double 

 cones are developed in place of the single one. Along 

 with these changes in the nucleus, others occur in the 

 protoplasm of the cell body, and its parts commonly dis- 

 play a tendency to arrange themselves in radii from the 

 extremities of the cones as a centre; while, as the separa- 

 tion of the two secondary nuclear spindles becomes com- 

 plete, the cell body gradually splits from the periphery 

 inwards, in a direction at right angles to the common 

 axis of the spindles and between their apices. Thus 

 two cells are formed, where, previously, only one existed ; 

 and the nuclear spindles of each soon revert to the 

 globular form and confused arrangement of the con- 

 tents, characteristic of nuclei in their ordinary state. 

 The formation of these nuclear spindles is very beau- 

 tifully seen in the epithelial cells of the testis of the 

 10 



