THE PROTOZOA 13 



retracting the hinder portion, the cell glides or flows along 

 from place to place. 



Upon meeting with any of the smaller organisms upon 

 which it lives, projections from the body are put out which 

 gradually flow around the prey and it becomes pressed into 

 the interior of the cell. The process is not unlike pushing 

 a grain of sand into a bit of jelly. There is no mouth. 

 Any point on the surface serves for the reception of food. 

 Oxygen gas also is taken into the body all over the surface, 

 and wastes and indigestible material are cast out at any 

 point. Nothing exists in these simple forms comparable to 

 the complex systems of organs that carry on these processes 

 in the squirrel. 



The bodily size of animals is limited, and to this general 

 rule the Amoeba is no exception, for upon gaining a certain 

 size, the nucleus divides into two exactly similar portions, 

 and very soon afterward the rest of the body separates into 

 two independent masses of equal size (Fig. 5, D), each of 

 which, when entirely free, contains a nucleus. In this way 

 two daughter amoebae are formed possessing exactly the 

 characters of the parent save that they are of smaller size ; 

 but it is usually not long before they reach their limit of 

 growth, when division occurs again, and so on, generation 

 after generation. 



It not infrequently happens, however, that the pond or 

 stream, in which the Amoeba and other Protozoa live, dries 

 up for a portion of the year. In such an event the body 

 assumes a spherical shape, develops a firm, horn-like mem- 

 brane about itself, and thus encysted it withstands the sum- 

 mer's heat and dryness and may be transported by the wind, 

 or otherwise, over great distances. When the conditions 

 again become favorable the wall ruptures and the Amoeba 

 emerges to repeat its life processes. 



15. Some relatives of the Amoeba. All amceba-like forms, 

 to the number of perhaps a thousand species, possess this 

 same method of locomotion, but many present some inter- 



