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. 
Fie. 2.— Amitosis. A. Division of blood-cells (a) Durin 8 
in the embryo chick, illustrating Remak's the pro phase 
quanie, ot mentees Sriien ihe chromatin 
division in the follicle cells of a cricket’s egg. granules which 
(From Dahlgren and Kepner, 1908.) 
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 (4, ¢; 
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- 
