WORMS. 



155 



on the hinder segments of the body prevent its stretching 

 backward, because the setae pointing backward stick into the 

 ground ; the body therefore can lengthen in only one direc- 

 tion, and that is in a forward one. Then, when the body 

 shortens, the setse in the forward segments stick into the 

 ground, and the hinder part of the body is drawn up, and 

 by this method the creature moves along. 



FIG. 143. EGG-CAPSULES or LEECH, A; AND YOUJJO LEECH, B. The egg-capsules are 

 drawn natural size. The young leech, which was taken from the egg-capsule, is drawn 

 greatly enlarged, the little line above showing its natural size. 



140. Another very common worm is the leech. Speci- 

 mens may be collected in almost any pond or lake, and kept 

 alive in jars of water. The creature is flat and broad, and 

 in some species is furnished, at the hinder end of the body, 

 with a sucker, while in others it has a sucker at each end of 

 the body. It crawls by means of these suckers, and swims 

 through the water by an undulating movement of the body. 

 The eggs of the leech are laid on the leaves and stems 

 of plants which grow in the water. The eggs are contained 

 in little oval and flattened capsules, and these capsules are 

 laid side by side. In Figure 143 A represents two capsules, 

 in which the little leeches can be seen ; B represents the 



figure of a young leech greatly enlarged, showing the eyes 

 8 



