14 



HEREDITARY CHARACTERS 



the chromatin is seen to arrange itself in a long coiled-up 

 thread within the nucleus (Fig. 2). This coiled-up thread 

 is known as the spireme. 1 At the same time that the spireme 

 is in process of formation, the two centrosomes are seen to 

 send out radiations into the surrounding cytoplasm. These 

 radiations are collectively known as " Asters" having been 



FIG. 1. A. Nuclear membrane. B. Masses of chromatin, joined 

 by threads of linin containing chromatin. C. Nucleolus. D. 

 Centrosomes, contained in E, the archoplasm. F. Contractile 

 vacuole. G. Food particles. H. Plastids. 



given this name on account of the appearance they present. 

 Some of these radiations extend between the two centro- 

 somes, thus forming a figure shaped like a spindle, made 

 up of a number of minute threads. As these radiations are 

 formed, the centrosomes begin to separate from each other, 

 gradually getting further and further apart (Fig. 2). Soon 



1 The formation of the spireme does not necessarily precede division in all 

 cells. It is, however, usual. 



