Fig. 50.—The Amœba, highly magnified
The amœba is observed to be a minute mass of protoplasm with an average diameter of about one-hundredth of an inch, endowed with a power of motion and locomotion. Its body is not uniformly clear, for the interior portion is seen to contain a number of minute granules, representing the undigested portions of the animal’s food. There is a small mass of denser protoplasm near the centre, termed the nucleus, and also a clear space filled with fluid. This latter is called the vacuole, and is probably connected with the processes of respiration and excretion, for it may be seen to contract at irregular intervals, and occasionally to collapse and expel its contents.
As we watch the amœba we see that it is continually changing its shape, sending out temporary prolongations (pseudopodia) of its gelatinous substance from any part, and sometimes using these extended portions for the purpose of dragging itself along.
Its method of feeding is as remarkable as it is simple. On coming in contact with any desired morsel, it sends out two pseudopods, one on each side of the food. These two pseudopods gradually extend round the food, till, at last, they meet and coalesce on the opposite side of it, thus completely enclosing it within the body. Any part of the body of the amœba may thus be converted into a temporary mouth; and, there being no special cavity to serve the purpose of a stomach, the process of digestion will proceed equally well in any part of the body except in the superficial layer, where the protoplasm is of a slightly firmer consistence than that of the interior. Further, the process of digestion being over, any portion of the superficial layer may be converted into a temporary opening to admit of the discharge of indigestible matter.
Fig. 51.—The Amœba, showing changes of form
