THE CELL. 35 



trosomes reach them they are called the polar bodies. In these situa- 

 tions they are surrounded by a more distinct zone of hyaloplasm 

 than that which enclosed the original parent centrosome, and beyond 

 this the spongioplasm is frequently arranged in radiations of unusu- 

 ally thick fibres. The polar bodies with their clear envelopes and 

 the prominent radiations about them are collectively known as the 

 attraction -spheres (Fig. 8). 



FIG. 8. 



Dividing cell from ovum of ascaris megalocephalus. (Kostanecki and Siedlecki.) a, polar body, 

 centrosome, surrounded by a clear zone ; 6, chromosomes of the dividing nucleus. Be- 

 tween the polar bodies is the achromatic spindle, and radiating from each attraction- 

 sphere are delicate filaments of spongioplasm. The cytoplasm presents indications of 

 vacuolation. 



While the polar bodies are separating, or after they have passed 

 into the polar regions of the cell, the nucleus begins to show those 

 changes in structure which constitute karyokinesis. This process 

 may be divided into a number of phases, as follows : 



1. The Formation of the Spirem (Fig. 9). This consists in a con- 

 densation of the chromoplasm. The branches of the nuclear fila- 

 ments are withdrawn into the substance of the main fibres, into 

 which the nuclear membrane or peripheral network bounding the 

 nucleus is also absorbed. The vesicular character of the nucleus is 

 lost during these changes in the arrangement of the chromoplasm, 

 which appears as a loose tangle or skein of one or more threads 

 of uniform diameter lying freely in the body of the cell. This 

 skein is called the spirem. The chromoplasm in this condensed con- 

 dition stains more deeply with nuclear dyes than in the resting con- 

 dition of the nucleus. The nucleoli in the meantime become faint 

 and seem to ultimately disappear. They play no part in the process 



