I NUTRITION 233 



The formation of the cyst is probably of great importance 

 in preserving the animalcule from destruction by drought, so 

 that should the pool in which it is living dry up, it may still 

 remain alive, protected by its shell-like case, until the con- 

 ditions for its active life are once more restored, when it 

 escapes from this encysted condition by the rupture of the 

 cell-wall. 



Very often an Amoeba in the course of its wanderings 

 comes in contact with a still smaller organism of some kind 

 or other. 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. 67, c, a). 

 The diatom or other organism becomes in this way com- 

 pletely enclosed in a cavity or food-vaciwle (/. vac), which 

 also contains a small quantity of water necessarily included 

 with the prey. The latter is taken in by the Amreba as 

 food : so that the Amoeba, like the frog, feeds. It is to 

 be noted that the reception of food takes place in a 

 particular way, viz. by ingestion — i.e. it is enclosed entire 

 by the organism. 



When the prey is thus ingested, its protoplasm becomes 

 digested, any insoluble portions being passed out or egested, 

 as fseces (p. 75), from the surface of the Amoeba as it creeps 

 slowly on. Note that all this is done without either ingestive 

 aperture (mouth), digestive cavity (stomacli), or egestive 

 aperture (anus) : the food is simply taken in by the flowing 

 round it of protoplasm, digested as it lies enclosed in the 

 protoplasm, and those portions for which it has no further 

 use are got rid of by the Amceba flowing away from them. 



We have seen that the frog possesses certain digestive 

 glands, the function of which is to secrete digestive fluids 

 which have an important chemical action on the food 



