The Life of the Individual 
95 
ated portion of the protoplasm which is especially active 
during the division of cells and carries the special organs 
(chromosomes), instrumental as the bearers of hereditary 
characters. The nucleus and surrounding protoplasm are 
closely united in their functions and are incapable of sepa¬ 
rate existence. The nucleus is, in its resting condition, 
usually rounded in form, while the remaining protoplasm 
is of various shapes according to the special functions of the 
cell. Protoplasm is characterized by ability to take in 
nourishment, to grow, 
to give off waste, to 
divide and to move in 
response to stimuli, but 
in each organ the cells 
become specialized to 
do some one thing es¬ 
pecially well and they 
often lose some of the 
functions of primitive 
protoplasm. For exam¬ 
ple, a nerve cell loses its 
power of contractility 
but becomes specialized 
for transmitting nervous 
impulses, while a muscle 
cell has a marked power of contractility. A detailed discus¬ 
sion of the structure and function of the various parts of 
the cell in different tissues is, of course, impossible here, 1 
but these few suggestions are sufficient to indicate the ex¬ 
treme complexity of the organization of each tissue that 
goes to make up any organism, such as the bee. 
The egg. 
The egg, as it leaves the ovaries of the queen where it is 
formed, is essentially a single cell. The eggs of most ani- 
1 The interested reader is referred to Wilson, E. B., The cell in development 
and inheritance. New York : Macmillan, and to other works on cytology. 
Fio. 50. — Group of tissue cells from skin 
of young salamander. 
