I MODE OF FEEDING 11 



becomes a globular mass around which is formed a thick, 

 shell-like coat, called the cyst or cell-wall (Fig. i, D, cy). 

 The composition of this is not known ; it is certainly not 

 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 

 its 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 send out pseudopods which gradually creep 

 round the prey, and finally unite on the far side of it, as in 

 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 neces- 

 sarily included with the prey. The latter is taken in by the 

 Amoeba as food : so that another function performed by the 

 animalcule 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. 



