THE PROTOZOA 13 
retracting the hinder portion, the cell glides or flows along 
from place to place. 
Upon meeting with any of the smaller organisms upon 
which it lives, projections from the body are put out which 
gradually flow around the prey and it becomes pressed into 
the interior of the cell. The process is not unlike pushing 
a grain of sand into a bit of jelly. There is no mouth. 
Any point on the surface serves for the reception of food. 
Oxygen gas also is taken into the body all over the surface, 
and wastes and indigestible material are cast out at any 
point. Nothing exists in these simple forms comparable to 
the complex systems of organs that carry on these processes 
in the squirrel. , 
The bodily size of animals is limited, and to this general 
rule the Ameba is no exception, for upon gaining a certain 
size, the nucleus divides into two exactly similar portions, 
and very soon afterward the rest of the body separates into 
two independent masses of equal size (Fig. 5, D), each of 
which, when entirely free, contains a nucleus. In this way 
two daughter amcebe are formed possessing exactly the 
characters of the parent save that they are of smaller size; 
but it is usually not long before they reach their limit of 
growth, when division occurs again, and so on, generation 
after generation. 
It not infrequently happens, however, that the pond or 
stream, in which the Ameéa and other Protozoa live, dries 
up for a portion of the year. In such an event the body 
assumes a spherical shape, develops a firm, horn-like mem- 
brane about itself, and thus encysted it withstands the sum- 
mer’s heat and dryness and may be transported by the wind, 
or otherwise, over great distances. When the conditions 
again-become favorable the wall ruptures and the Amba 
emerges to repeat its life processes. 
15. Some relatives of the Ameeba.— All amceba-like forms, 
to the number of perhaps a thousand species, possess this 
same method of locomotion, but many present some inter- 
