GENERAL SKETCH 



49 



minute beings absorbs and completes their entire existence. This 

 function assumes with them an intensity which, I believe, is equalled 

 nowhere else in the animal kingdom. They are gluttons par excel- 

 lence, absorbing and digesting night and day without repose. It 

 results that the apparatus charged with the performance of such 

 an intense function becomes modified, diversified, and developed to 

 an astonishing degree, especially striking when it is remembered that 

 these are unicellular organisms." J 



The capture and ingestion of food, in its simplest form, occurs in 



Fig. 18. Food-taking. [A, PENARD; B and C, BUTSCHLI.] 



A. Raphidiophrys elegans Hert. and Lesser. B. Oikomonas termo Ehr. C. Didinum nasutum, 

 O.F.M. f, food particles. 



the group of Rhizopoda, where, as in Amazba proteus, any part of the 

 body can act as a mouth. In this form pseudopodia are pushed out 

 toward the victim (a flagellate, ciliate, minute plant form of any 

 kind, or even a higher animal, such as a rotifer or worm) and entirely 

 surround it, together with a certain amount of water, thus forming a 

 gastric vacuole, or an improvised " stomach." When the rhizopod is 

 provided with a shell, the food-taking afea is limited to a mouth-open- 

 ing in the shell, while in many of the shelled Heliozoa the taking of 

 food is complicated by the presence of an unbroken coating, and a 

 special opening must be made for each ingestion (Fig. 18). In the 

 Reticulariida, the gastric vacuoles are on the outside of the shell, and 

 are formed in the network produced by the anastomosis of the pseu- 



E i ('88), p. 185. 



