IN THE FIELD 221 



experiment, says : " Most of the harm they do is strikingly 

 noticeable and is of short duration, while the good is per- 

 petual from spring to fall, but is in no way noticeable and 

 cannot well be estimated." 



See Bulletin No. 6, Iowa Agricultural Experimental Station. 



39. The Earthworm. 



MATERIAL : Earthworms on moist soil in a small dish. Previously 

 observed : Tracks of the worms after a rain ; worms creeping about 

 on wet soil, boards, or stones ; castings over their holes ; leaves and 

 straws drawn into their holes. 



You know that birds and mammals have an internal bony 

 skeleton, which gives them a solid frame for the whole 

 body; insects and crabs have 110 bones, but they have a 

 hard external covering by which the soft, inner parts are 

 protected, and to which their muscles are attached. How 

 much the earthworm differs from all these animals ! It has 

 no legs, no bones, no hard carapace like the beetle ; its body 

 is simply a bundle of muscles covered by a soft skin. 



How can the earthworm move ? If you are close observers, 

 you have seen that the whole body consists of a large num- 

 ber of rings, and that the worm can contract and extend 

 itself very much. Along the sides and below you can see, 

 and feel still better, a large number of short bristles, which 

 keep the worm from slipping back as it crawls by extend- 

 ing and contracting itself. Have you ever tried to pull 

 earthworms out of their holes ? If you did, you must have 

 found that their strength is considerable. By means of their 

 numerous bristles, and by contracting their muscles, they 

 often escape into their holes when the boys attempt to pull 

 them out. 



In spite of a host of enemies, earthworms are abundant 

 wherever a rich soil furnishes them food. 



At what time do the various seeds mature ? 



