I MODE OF FEEDING 11 



protoplasmic, and very probably consists of some nitrogenous 

 substance allied in composition to horn and to the chitin 

 which forms the external shell of Crustacea, insects, &c. 

 After remaining in this encysted condition for a time, the 

 Amoeba escapes by the rupture of its cell-wall, and resumes 

 active life. 



Very often an Amoeba in the course of its wanderings 

 comes in contact with a still smaller organism, such as a 

 diatom (see Lesson XIV., Fig. 35) or a small infusor (see 

 Lessons X. XII.). When this happens the Amoeba may 

 be seen to extend itself round the lesser -organism until the 

 latter becomes sunk in its protoplasm in much the same way 

 as a marble might be pressed into a lump of clay (Fig. i, 

 c, a). The diatom or other organism becomes in this way 

 completely enclosed in a cavity or food-vacuole (f. vac), 

 which also contains a small quantity of water necessarily in- 

 cluded with the prey. The latter is taken in by the Amoeba 

 as food : so that another function performed by the animal- 

 cule is the reception of food, the first step in the process of 

 nutrition. It is to be noted that the reception of food takes 

 place in a particular way, viz. by ingestion i.e. it is enclosed 

 raw and entire in the living protoplasm. It has been noticed 

 that Amoeba usually ingests at its hinder end that is, the 

 end directed backwards in progression. 



Having thus ingested its prey, the Amoeba continues its 

 course, when, if carefully watched, the swallowed organism 

 will be seen to undergo certain changes. Its protoplasm 

 is slowly dissolved ; if it contains chlorophyll the green 

 colouring matter of plants this is gradually turned to brown ; 

 and finally nothing is left but the case or cell-wall in which 

 many minute organisms, such as diatoms, are enclosed. 

 Finally, the Amoeba, as it creeps slowly on, leaves this empty 

 cell-wall behind, and thus gets rid of what it has no further 



