242 



RECENT CYTOLOGY 



and a paternal member fused together. Each of the 

 visible chromatic bodies next divides into four parts, 

 the set of four deeply staining bodies being known as a 

 tetrad. Thus when there are four somatic chromosomes 

 the number of tetrads appearing will be two (Fig. 32). 

 A mitosis now takes place, during which there is no 

 further division of chromosomes, but half of each 



Fig.32 



Fig. 35 



Fig.36 



tetrad passes to either pole of the nuclear spindle, 

 so that each daughter nucleus comes to contain two 

 half-tetrads, each consisting of a pair of deeply-staining 

 bodies (Fig. 34). This division is not followed by the 

 production of a resting nucleus, for before any nuclear 

 reticulum is formed, and while the half-tetrads still 

 retain their definite appearance, the daughter nuclei 

 divide again. At this second division in each nucleus 



