THE WORMS 



213 



or straw, one end will be found to respond much more readily to 

 touch than the other end. The more sensitive end is the front 

 or anterior end, the other end being the posterior end. Jar the 

 dish in which the worm is crawling; it will immediately respond 

 by contracting its body. 



Living earthworms tend to collect along the sides of a dish or in 

 the corners. This seems to be due to an instinct which leads them 

 to inhabit holes in the ground. 



An earthworm placed half in and half out of a darkened box soon 



An earthworm crawling over a smooth surface. 



responds by crawling into the darkened part and remaining there. 

 There are no eyes visible. A careful study of the worm with the 

 microscope, however, has revealed the fact that scattered through 

 the skin, particularly of the anterior segments, are many little struc- 

 tures which not only enable the animal to distinguish between 

 light and darkness, but also light of low and high intensity, as well 

 as the direction from which it comes. A worm has no ears or 

 special organs of feeling. We know, however, that although a 

 worm responds to vibrations of low intensity, the sense of touch is 

 well developed in all parts of the body. 



It also responds to the presence of food, as can be proved if 

 bits of lettuce or cabbage leaf are left overnight in a dish of 

 earth where worms are kept. 



Locomotion of an Earthworm. If we measure an earthworm 

 when it is extended and compare with the same worm contracted, 

 we note a difference in length. This is accounted for when we 

 understand the method of locomotion. Under the skin are two 

 sets of muscles, an outer set which passes in a circular direction 



