r PHYLUM PROTOZOA 17 



say, a fifth of the total diameter of the Amceba, when by a 

 sudden contraction of its walls, it suddenly disappears, to 

 reappear presently and gradually grow again to its maxi- 

 mum size. This pulsating clear space is the contractile 

 vacuole. 



By watching the Amceba 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 con- 

 nected 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 Amceba, — into the interior of the protoplasm. 

 A process of the protoplasm is pressed against such a par- 

 ticle 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 pro- 

 toplasm into the surrounding water. The matter which dis- 

 appears evidently mixes with the protoplasm and adds to its 

 bulk. 



When food is abundant the Amceba increases in bulk — 

 more food being ingested than is required for simply main- 

 taining the size unaltered — and soon a remarkable change 

 takes place. The processes become withdrawn, and a fissure 

 appears dividing the Amceba 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 dis- 

 tinct 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 two new 

 Amcebse possesses a nucleus similar to the original one, 

 c 



