2), which is commonly present in freshwater ponds, may be used.

This appears as a small mass, seemingly of gelatinous consistency with a clear outline, the exterior part homogeneous, the interior granular.

The nucleus, which is seen with difficulty, appears as a small vesicle in the interior.

Many amoebae show also in the interior a small clear space, the contractile vesicle which alternately contracts and expands, through which action the movement of the intracellular fluid is facilitated and waste products removed.

The interior granules often change their position, showing that there is motion within the mass.