SEXUAL REPRODUCTION. 43 
After resting and growth of the segmentation-nucleus 
a series’ of cell-divisions takes place called segmentation. 
These cell-divisions continue throughout the life of the 
individual, but the earlier and more evident divisions are 
called segmentation. 
We may illustrate the process of sexual reproduction 
thus— 
Fig. 15.—DIAGRAM ILLUSTRATING NUCLEAR CHANGES DURING 
: “SEXUAL REFRODUCTION. 
MALE. FEMALE. 
Primitive germ cell grows 
to form sperm-mother N N. 
COL iced Sere eeisieieaters oe 
Primitive germ cell grows 
Sperm-mother cell divides to form egg-mother cell. 
into two... ...... Egg-mother cell divides 
into two. 
“4 And four to form ovum 
N and two polar bodies. 
And into four to form four 
spermatozoa .........+ 
wiz 
Spermatozoon and ovum 
fuse. 
> Cell-divisions. 
After hundreds of these cell-divisions, one N. becomes 
the nucleus of a primitive germ-cell, increases to 2N. in the 
mother cell, leaves the organism as ¥ in the pronucleus, 
and the cycle recommences. 
If this diagram be carefully studied it will be clear 
that the process of maturation has for its object the forma- 
tion of cells which have only half the usual nuclear element, 
whereas fertilisation consists of the fusion of these halves to 
form nuclei of normal proportions. Further, the dimorphism. 
