86 PROTOZOA. 
Tf the outline of an Ameba be sketched every few 
seconds and the series of drawings examined, it 
will be seen that the shape has undergone con- 
siderable change, and it will also probably be 
found that the whole animal has moved somewhat from 
its original position. 
Further, this. peculiar change of shape is evidently due 
to the pushing outwards of processes, which gradually 
grow larger and larger. If a drop of treacle 
be placed on a flat surface and the surface 
gently inclined, the drop will progress in a similar fashion 
External 
Features. 
Movements. 
Fig. 28.—Ama@BaA Proteus (Magnified). 
A large diatom is enveloped on the left. The largest sphere 
is the contractile vacuole ; the smaller is the zucleus. 
by processes thrust out in the direction of least resistance ; 
but the treacle processes differ from those of Ameda, 
because in the former the energy for such movement is 
derived from without (the acceleration due to gravity), 
and they are hence only in a downward direction, 
whereas in the latter the energy is provided by the 
chemical decomposition of the protoplasm itself, hence 
their direction is determined by other factors and the 
