26 



THE HEL1OZOA 



subsequently divides into two parts, which travel to opposite poles 

 of the nucleus. The nucleus now begins to increase considerably 

 in size, and is- seen to contain several large chromatin bodies which 

 certainly contain both chromatin and plastin derived from the 

 nucleoli (Fig. 5, II). The centrosomes at each pole of the 

 nucleolus are of considerable size and more conspicuous than at 

 any other time in the divisions of the three kinds of karyokinesis. 

 The chromosomes are now formed by a breaking down of the 



Fio. 5. 



ActinospJiaerium. Formation of the second polar spindle. I, the nucleus after the first 

 polar division, the centrosome (c) reduced in size previous to the formation of the second 

 polar figure. II, the same nucleus at a later stage with two centrosomes. Ill, IV, V, VI, 

 VII, stages in the formation of the second polar nucleus. (After II. Hertwig.) 



chromatin masses, and gradually assume an equatorial position. 

 They are at first very irregular and angular in shape, but ultimately 

 become rod-shaped, constrict in the middle, and divide transversely. 

 The spindle fibres seem to be formed from the achromatic network, 

 and several plastin remnants remain in the nucleus during the 

 formation of the chromosomes. The chromosomes now travel 

 towards the opposite poles of the spindle in the usual way 

 (Fig. 5, VI), and subsequently become arranged in a fan-shaped 

 manner at the extremities of the now elongated spindle. According 



