154 ANARTHROPODA 



eye. Between the ninth and eleventh somites are two 

 pairs of openings from which sperm cells enter the band 

 and render the several eggs fertile. As the band slips off 

 the head it is changed into a closed capsule within which 

 only one worm develops, the others being devoured by 

 the sole survivor. 



For dissection, a worm over five inches long should be 

 pinned ventral side down in a pan of water and a slit made 

 with the scissors through the body wall in the anterior 

 half along the mid-dorsal line. Pin down the body walls 

 on either side and note the parts as shown in the figure. 

 The blood runs forward in the dorsal vessel and backward 

 in the ventral one. No true heart is present, but the five 

 pairs of aortic arches are contractile. The paired nephridia 

 in each somite are the kidneys, which conduct the waste 

 matter outside of the body. The worm has no tracheal 

 tubes, gills, or lungs, but receives oxygen into the blood 

 and casts out the carbon dioxide by means of the small 

 vessels ramifying near the surface. 



Earthworms feed on decayed leaves and other vegetable 

 matter. They are of much service in keeping the soil 

 loose and permitting the water and air to penetrate to the 

 roots of plants by means of their burrows. They also 

 make good food for birds. Their power of regeneration 

 after injury is remarkable. If one be cut in two near the 

 middle each half will often develop into a complete worm. 

 The power to regenerate lost parts is much greater in the 

 lower animals than in the higher ones. A tadpole may 

 regenerate a lost leg but not a half or even a fourth of its 

 body, while a mammal can not reproduce even a fourth of 

 a finger or toe removed, 



