14 



GERM-CELL CYCLE IN ANIMALS 



nucleolus. As we shall see later (Chapter V) , amitosis 

 has been described in cells of the germ-cell cycle, 

 and must therefore be reckoned with in any discus- 

 sion of the phys- 

 ical basis of 

 heredity. 



Mitosis or ka- 

 ryokinesis in- 

 volves a rather 

 complicated 

 series of pro- 

 cesses which 

 cannot be fully 

 discussed here 

 but will be out- 

 lined very briefly 

 with the aid of 

 Fig. 3. 



(a) During 

 the prophase 

 the chromatin 

 granules which 

 are scattered 

 through the nucleus in the resting cell (^4) become 

 arranged in the form of a long thread or spireme (B). 

 At the same time the centrosomes move apart (A, c; 

 B, a), and a spindle arises between them (C). While 

 this is going on, the nuclear membrane generally 

 disintegrates and the spireme segments into a num- 

 ber of bodies called chromosomes (C) ; these take a 

 position at the equator of the spindle, halfway be- 



FIG. 2. Amitosis. A. Division of blood-cells 

 in the embryo chick, illustrating Remak's 

 scheme, a e = successive stages of division. 

 (From Wilson, 1900.) B. Amitotic nuclear 

 division in the follicle cells of a cricket's egg. 

 (From Dahlgren and Kepner, 1908.) 



