50 COMPARATIVE ZOOLOGY. 



tube. Thus, we find a mouth, or sucker, furnished with 

 teeth for lancing the skin of animals, as in the Leech ; a 

 bristle-like tube fitted for piercing, as in the Mosquito; a 

 sharp sucker armed with barbs, to fix it securely during 

 the act of sucking, as in the Louse; and a long, flexible 

 proboscis, as in the Butterfly (Fig. 23). Bees have a hairy, 

 channelled tongue (Fig. 22), and Flies have one terminat- 

 ing in a large fleshy knob, with or without little "knives" 

 at the base for cutting the skin (Fig. 24) ; both lap, rather 

 than suck, their food. 



Most animals drink by suction, as the Ox; and a few 

 by lapping, as the Dog; the Elephant pumps the water 

 up with its trunk, and then pours it into its throat; and 

 Birds (excepting Doves) fill the beak, and then, raising 

 the head, allow the water to run down. 



Many aquatic animals, whose food consists of small par- 

 ticles diffused through the water, have an apparatus for 

 creating currents, so as to bring such particles within 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 cir- 

 culate through the system of canals traversing its body 

 by the vibration of minute hairs, or cilia, lining parts of 

 the canals (Fig. 189). The microscopic Infusoria have 

 cilia surrounding the mouth, with which they draw or 

 drive into the body little currents containing nutritious 

 particles. Bivalve mollusks, as the Oyster and Clam, are 

 likewise dependent upon this method of procuring food, 

 the gills 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. 282). 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. 342). 



