ies aes 
THE 
AMERICAN NATURALIST 
VoL. XXV. JUNE, 1891. 294. 
WANDERING CELLS IN ANIMAL BODIES. 
BY J. L. KELLOGG. 
1e some of the surface sediment ofa quiet fresh-water pond be 
examined under the microscope, one would very likely find a 
curious, colorless organism, containing a number of granules, and 
perhaps now and then a microscopic plant. A little observation 
will show this animal—for such it is—to be merely a mass of pro- 
toplasm which possesses the power of changing its shape by the 
protrusion of any part of its body in irregular branches, or thin, 
fine filaments. By means of these, it is able to move very slowly 
from place to place, forcing its way between particles of dirt 
which surround it, and also to take in solid food. This latter 
process is accomplished by a covering over or flowing about a 
piece of food by the thin, jelly-like body. When the food is thus 
covered over, the fluid protoplasm of the animal, which is called 
an amæba, is seen to possess the power of truly digesting the 
food which it holds. This process, taking place in a single unspe- 
cialized or undifferentiated cell, is called intracellular digestion. 
The ameeba is, in its structure, a single cell, comparable to any 
one of the myriads of cells that go to make up the body of one 
of the higher animals. These cells may lose, in a higher organ- 
ism, the simple amceboid form, and assume complex shapes and 
functions in different parts of the body; generally ‘losing, also, 
the power of movement. Many, however, retain the power of 
moving under proper stimuli,—as, for example, the cells that go 
