HOW ANIMALS EAT 251 



their reach. This is particularly true of low, fixed forms, 

 which are unable to go in search of their food. Thus, 

 the sponge draws nourishment from the water, which is 

 made to circulate through the system of canals travers- 

 ing its body by the vibration of flagella, lining parts of the 

 canals (Figs. 14, 15). The microscopic infusoria have 

 cilia surrounding the mouth, with which they draw or 

 drive into the body little currents containing nutritious 

 particles (Figs. 9, n). Bivalve mollusks, as the oyster 

 and clam, are likewise dependent upon this method of 

 procuring food, the gills and inner surface of the 

 mantle being covered with cilia. So the singular fish, 

 amphioxus (the only example among vertebrates), em- 

 ploys ciliary action to obtain the minute organisms on 

 which it feeds (Fig. 117). The Greenland whale has a 

 mode of ingestion somewhat unique, gulping great vol- 

 umes of water into its mouth, and then straining out, 

 through its whalebone sieve, the small animals which 

 the water may contain (Fig. 171). 



(2) Solids. When the food is in solid masses, whether 

 floating in water or not, the animal is usually provided 

 with prehensile appendages 

 for taking hold of it. The 

 jellylike amoeba (Fig. i) has 

 neither mouth nor stomach, 

 but extemporizes them, seiz- 

 ing its food by means of its 

 soft body. The food then 

 passes through the denser, 



, , FIG. 213. A Foraminifer (Rotalia 

 OUter portion OI the body Veneta~), with pseudopodia extended, 



into the softer interior, where 



it is digested. The waste particles are passed out in 

 the reverse direction. In the foraminifers, threadlike 

 projections (pseudopodia) of the body are thrown out 

 which adhere to the prey. The soft jellylike substance 



