8 THE ORIGIN OF PLANT AND ANIMAL CHILDREN 
Figure 9.—The Matu¬ 
ration Division of the 
Egg Cell. 
In the first stage the 
star-like central body 
has divided. In the sec¬ 
ond stage the nucleus 
has divided and one half 
the color bodies are being 
expelled. In the third 
a spermatozoon is enter¬ 
ing the egg cell to ferti¬ 
lize it. In the fourth 
stage the nucleus is 
shown with the full num¬ 
ber of color bodies, two 
of which are from the 
spermatozoon. 
2. What are bisexual animals called ? 
3. What is a perfect flower ? 
4. What is an ovary? 
5. What is a testis ? 
Chromosomes. — To understand 
something of the deep significance of 
sexual reproduction, it will be necessary 
to study something of the structure of 
the nucleus. As a cell prepares to di¬ 
vide in growth, the tiny granules which 
are in the nucleus arrange themselves 
in lines, called color bodies ( chromo¬ 
somes ) since, when stained, they take a 
deeper color than the remainder of the 
cell. Every plant and every animal 
has a certain distinctive number of color 
bodies in each nucleus. Some organ¬ 
isms, as certain worms, have a small 
number, four, while others have more 
than a hundred and fifty. The human 
cell has twenty-four, according to some 
authorities. When the cell divides in 
growth, every color body divides in two, 
thus maintaining in each nucleus the 
distinctive number of chromosomes. 
1. What are chromosomes? 
2. How many chromosomes are in a nu¬ 
cleus? 
3. What change do the chromosomes 
undergo when the cell divides? Figure 8. 
Inheritance. — We shall next consider 
the part these color bodies play in re¬ 
production. As the egg cell prepares 
(a process called maturation) for union 
with the sperm cell, it divides in such 
