DIVISION OF LABOR 
153 
illustrated in rowing. Eight men in a large rowing shell 
can go faster than one man in a single, small shell. In repro¬ 
duction, the sixteen cells fall apart, and each one grows into 
a new colony. 
130. Volvox.— Volvox. is a colony of hundreds of tiny 
green cells embedded in a hollow gelatinous sphere. Each 
cell has two flagella. For a time all the cells are alike and 
share equally in the work of the colony. But in reproduction 
only a few cells take part. In the simplest method, a few 
cells grow large and escape into the hollow sphere. There, 
they divide and grow into new 
colonies. Finally, the mother 
colony breaks, and the daughter 
colonies escape. 
The more complex method is 
like the reproduction of higher 
animals. Certain cells in the 
colony grow large and escape 
into the hollow sphere. They 
are the egg cells. Other cells of 
the colony enlarge and divide 
into large numbers of slender, free-swimming cells called 
sperm cells. The sperm cells escape into the hollow sphere 
and swim about. One sperm enters an egg cell and unites 
with it, forming a single cell, the fertilized egg cell, which 
can develop a new colony. 
131. Division of Labor. — In gonium, the cells are alike in 
form and function, but in volvox, we find that a few cells 
have been changed in form in order to perform better the 
special work of reproduction. This is the first step in the 
division of labor. 
This is well shown in the higher animals, where certain 
cells are grouped together for a given work. The diges¬ 
tive system contains cells which work to make solutions of 
the food eaten. These solutions nourish the whole body, 
