212 GENERAL ZOOLOGY 



vary greatly in their food habits. Some live largely on 

 insect larvae (Fig. 85, C), others are scavengers, bub the 

 most important are blood suckers. Some of the blood 

 suckers puncture the skin with a muscular proboscis, others 

 bite a hole with three small teeth. A substance is secreted 

 which inhibits the coagulation of the blood, so that there 

 may be no interference with feeding. The alimentary canal 

 is large and has several side pockets. When an opportunity 

 occurs, a leech gorges itself and is then able to go for several 

 months without food. 



The breeding habits of leeches are of particular interest. 

 In some species one individual sticks a packet of sperm on 

 the outside of another, and the spermatozoa bore in through 

 the skin. This unique method of fertilization is known as 

 hypodermic impregnation. Many leeches produce cocoons 

 Jike those of earthworms which are stuck on the underside 

 of rocks (Fig. 85, E); others carry the eggs and young 

 fastened to the ventral side of the body (D). 



