230 
HAROLD’S DISCUSSIONS. 
The ameba has been described in Cliapter XXIL 
A study of this simple cell with a compound micro¬ 
scope reveals much that is suggestive. We may see 
it begin to divide. The mother cell separates into 
two equal cells. Each has its nucleus and threads. 
Evidently the mother-cell has divided the threads and 
given each daughter-cell half. They are therefore 
like their mother in every respect. Between them 
they have inherited their mother entire. 
We may examine a vorticella in a drop of stag¬ 
nant water, one of another class of simple one-celled 
animals. In shape it is like a bell (Fig. 112); at one 
end it has a short stem, by means of which it was at¬ 
tached to a dead leaf in the water. As I watch it 
with the microscope I notice that it divides like the 
ameba, but lengthwise. The two halves are upon the 
same stem. Soon one of them frees itself, and by 
means of a circle of very fine hairs called cilia, it 
paddles oli in the drop of water. Here again the 
mother-cell has divided and become two daughter- 
cells. 
Close by this is another vorticel. Instead of 
dividing into two equal parts, it sends out a little bud 
on the side, which separates from the mother-cell as 
soon as it has developed its cilia, and then swims 
away. 
This manner of reproduction, however, does not 
go on indefinitely. Exhaustion seems to take place 
in the course of two or three generations. Then two 
vorticellge unite and each gives up a part of the con¬ 
tents of its nucleus to the other. The cells that unite 
