ANIMAL LOCOMOTION 201 



Caterpillars resemble earthworms on account of 

 their bodies being divided into numerous segments 

 or movable rings, but they differ in the fact that 

 they also possess a number of legs, as many as 

 sixteen sometimes being present. The majority 

 of them creep along with an undulating and crawling 

 motion, but the loopers, geometers, or span-worms as 

 they are called in America, are unable to crawl 

 because the middle portion of their bodies is unpro- 

 vided with legs. When walking they progress in a 

 series of looping strides, grasping firmly with their 

 single pair of hind legs or prolegs, as well as with 

 their two claspers, as the terminal pair of leg-like 

 members are termed ; then stretching out their 

 bodies and talking hold with their three pairs of fore- 

 legs or true legs, after which they proceed to unclasp 

 their hind legs and, arching their bodies, place them 

 close to the front ones. 



The octopus, the cuttle-fish or sepia, the squid, 

 the nautilus, and the argonaut progress in a very 

 curious manner, for when swimming they propel 

 themselves backwards by means of expelling water 

 through a funnel-like organ known as a siphuncle, 

 a performance that may be likened unto a rocket 

 being lifted upwards and backwards into the air 

 by the force of the discharge of the chemical com- 

 pounds contained within its outer wrapper. The 

 creatures employ their arms or tentacles, however, 

 for the purpose of walking and climbing, and when 

 progressing along the bed of the ocean they proceed 

 head downwards. 



In former days it was believed that the argo- 



