194 INVERTEBRATE ZOOLOGY 
SARCODINA 
A NAKED RHIZOPOD. AMOEBA 
The amoeba is a jelly-like, single-celled animal which may be 
found in stagnant water attached to submerged objects, or in 
bottom sediment; it is also often found in moist, damp places 
which are not under water. The animals are very variable in 
size, the largest being within the range of the unaided vision, 
the smallest species requiring high powers of the microscope 
to detect. 
Mount on a slide a drop of water with sediment or scrapings 
from a submerged leaf or stick containing amoebas, and find 
one. Observe its shape and granular appearance. From time 
to time the shape of the body changes by the thrusting out 
of projections called pseudopodia. Observe the formation of 
pseudopodia. ; 
Exercise 1. Draw several outlines of the animal, showing its 
shape at different times. 
Observe the structure of the body. The protoplasm forming 
it will be seen to be divisible into two layers, the ectosarc 
and the entosarc; the former is the clear, transparent layer 
which forms the periphery of the body; the latter is the gran- 
ular, translucent mass which forms the remainder of it. The 
ectosare is of firmer consistency than the entosarc and secretes 
a delicate cuticula on its outer surface. When a pseudo- 
podium begins to form, it consists at first of ectosare alone, 
but entosare finally enters it as it grows larger. The entire 
body will often flow into a single pseudopodium, in which case 
