I PHYLUM PROTOZOA 17 



will be observed to increase gradually in size till it reaches a 

 maximum of, let us say, a fifth of the total diameter of the 

 Amoeba, when by a sudden contraction of its walls, it 

 suddenly disappears, to reappear presently and gradually 

 grow again to its maximum size. This pulsating clear 

 space is the contractile vacuole. 



By watching the Amoeba carefully for some time we may 

 be enabled to observe that the movements of the proto- 

 plasm of the body not only effect locomotion, but are 

 connected also with the reception of certain foreign particles 

 of organic nature i.e. either entire minute animals or 

 plants, or minute fragments of larger forms which form the 

 food of the Amoeba, into the interior of the protoplasm. 

 A process of the protoplasm is pressed against such a 

 particle of food, which becomes sunk in the soft substance, 

 and passes gradually into the interior. Here it becomes 

 surrounded by a little globule of watery fluid, and by 

 degrees partially or wholly disappears ; the part, if any, 

 which remains, subsequently passes outwards from the 

 protoplasm into the surrounding water. The matter which 

 disappears evidently mixes with the protoplasm and adds to 

 its bulk. 



When food is abundant the Amoeba increases in bulk 

 more food being ingested than is required for simply 

 maintaining the size unaltered and soon a remarkable 

 change takes place. The processes become withdrawn, and 

 a fissure appears dividing the Amoeba into two parts (Fig. 

 2). This fissure grows inwards, and the two parts become 

 more and more completely separated from one another, till 

 eventually the separation becomes complete, and we have 

 two distinct Amoebae resulting from the division of the one. 

 While the protoplasm has been undergoing this division 

 into two halves, the nucleus also divides, and each of the 



Man. Zool. C 



