198 From Matter to Man. 



quickly in the water. The motive machinery is con- 

 tained in the innumerable muscles which form the 

 ring-walls of its body, each worked by a system of 

 nerves, connected with knots or nerve-centres down 

 its back, and directed from a chief-centre in the head 

 as a brain. It is also provided with suckers at either 

 end for fastening itself. Intelligence, it will be 

 observed, increases with the increase of sense organs, 

 and, consequently, more complex machinery to work 

 both senses and muscles. 



The earthworm also progresses like the leech, but, 

 in addition, it possesses incipient legs, in the shape of 

 four pairs of bristles on each ring of its body. These 

 are not used for walking, but for gripping the sides 

 of its tunnel when boring with its head. Though 

 blind and deaf, its sense of touch is highly developed, 

 the slightest vibration on the ground sending it 

 instantly to cover. It also grows a new tail when the 

 old one has supplied the early bird with its breakfast. 

 The mend is sometimes performed very clumsily too ; 

 but this may depend upon the nature of the amputa- 

 tion. Some marine worms use their bristles for 

 walking. Others develop complicated machinery for 

 other life-purposes — gills for breathing, aerating the 

 blood, etc. 



Caterpillars. — A curious development of locomotion 

 characterises the " inch " caterpillar, which progresses 

 by measuring its length at every stride. Other 

 caterpillars and centipedes develop feet on each ring 

 of their bodies. But, while this mode of pedestrianism 



