DESCRIPTION OF PLATES. 125 
Amapa. (Puats IL, Fie. 1.) 
The Amoebee are frequently spoken of as little 
masses of living protoplasm without organization. 
This is not quite true, for in Amoeba the external 
surface of the protoplasmic mass has a little more 
consistence than the interior, and serves the pur- 
pose of a limiting membrane ; while in the interior 
may be seen a flattened sphere of granular ma- 
terial, — the nucleus, — and a cavity — the contractile 
vesicle — which contracts and expands in a rhyth- 
mical manner, and contains a watery fluid. The 
denser external layer of protoplasm, however, dift 
fers from a membranous envelope, inasmuch as it 
may be perforated at any point without injury, as 
the fissure is immediately closed by the coalescence 
of its margins. This is seen in the taking of food 
and rejecting of effete material from the body of 
the animal. Food particles are admitted through 
any part of the exterior of the body with which 
they chance to come in contact, there being no 
mouth and no digestive cavity; and undigested 
remnants are rejected in the same way. 
That the nucleus and contractile vesicle are 
not organs necessary to the creature in sustain- 
ing its independent existence, is shown by the 
fact that a little mass of the protoplasm detached 
by accident becomes at once an independent 
amoeba, fully able to shift for itself, in which 
subsequently a nucleus and a contractile vesicle 
may appear. 
The ameceba not only eats without a mouth and 
