WORMS. 



155 



on the hinder segments of the body prevent it stretching 

 backward, because the setae pointing baclcward stick into the 

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

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

 shortens, the setaa 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. 



A B 



Pig. 143. — Egg-Capsules of Leech, A ; and Young Leech, B — The egg-capsules arc 

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

 greatly enlarged, the httle 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 others have 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 cap- 

 sules are laid side by side. In Figure 143 A represents two 

 capsules, in which the little leeches can be seen ; and also a 

 figure of a young leech greatly enlarged, showing the eyes 



