16 GERM-CELL CYCLE IN ANIMALS 
surrounded by a number of radiating astral rays, and 
a spindle which lies between them. The chromo- 
somes lie in the equatorial plate (ep). 
(b) During the second stage, the metaphase, the 
chromosomes split in such a way that each of their 
parts contains an equal amount of chromatin (FE, ep). 
As we shall see later, this is one of the most significant 
events that takes place during mitosis. 
(ec) During the anaphase (F) the chromosomes 
formed by splitting move along the spindle fibers 
to the centrosomes. As a result every chromosome 
present at the end of the prophase (D) sends half of its 
chromatin to either end of the spindle. The mechan- 
ism that brings about this migration is as yet some- 
what in question. Fibers are usually left between 
the separating chromosomes; these are known as 
interzonal fibers (F, if). 
(d) The telophase (G, H) is a stage of reconstruction 
from which the nuclei emerge in a resting condition; 
the chromatin becomes scattered through the nucleus, 
which is again enveloped by a definite membrane 
(H); the centrosome divides and, with the centro- 
sphere, takes a position near the nucleus. Finally 
the cycle is completed by the constriction of the cell 
into two daughter cells. 
There are a number of differences between the 
sort of mitosis just described and that which occurs 
during the maturation of the egg and spermatozoin ; 
these and certain other phases of cell division will 
be considered in their appropriate places in succeed- 
ing chapters. 
