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. 2S2). 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). 
