THE PROTOZOA OF THE SEA SHOEE 103 



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 amosba 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 



FIG. 51. THE AMOSBA, SHOWING 

 CHANGES OF FORM 



Fio. 52. THE AUCEBA, 



FEEDING 



on the opposite side of it, thus completely enclosing it within the 

 body. Any part of the body of the amoeba 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. 



The amceba is an omnivorous feeder, but subsists mainly on 

 vegetable organisms, especially on diatoms and other minute 

 algae ; and the siliceous skeletons of the former may often be seen 

 within the body of the animal, under the high power of a micro- 

 scope. 



The multiplication of the amoaba is brought about by a process 

 of fission or division. At first the nucleus divides into two, and 



