V 

 VI INTRODUCTION. 



common in Khizopods, as well as in many forms of 

 Infusoria. Its true nature is not fully understood. It is 

 usually situated near the border of the endosarc, often 

 opening in the ectosarc, as in some of the Heliozoa 

 the common Actinophrys, for example. The pulsat- 

 ing vesicles slowly enlarge until they attain a certain 

 size, after which they suddenly collapse and entirely 

 disappear ; and this operation is repeated with a degree 

 of regularity. 



The food of Rhizopods usually consists of diatoms, 

 desmids, and other algae, and fragments of higher plants. 

 Within the body the food is usually accumulated in 

 spherical masses, which may be green, brownish or red ; 

 depending upon its nature and the changes which it 

 undergoes during digestion. Ehrenberg supposed that 

 the sperical masses indicated so many stomachs, and 

 therefore regarded the Rhizopods as belonging to his 

 Polygastrica. It is probable that the food is simply 

 enveloped by the protoplasm and becomes digested, after 

 which the hard portions may be thrown out at any part 

 of the surface of the body. 



The most commonly observed process of multiplica- 

 tion is by division ; in some species the body becomes 

 encysted, but the entire process has not yet been fully 

 made out. 



Rhizopods are far more common in the ordinary col- 

 lections of the microscopist than is generally supposed, 



