156 INSECTS ANNELIDA DIAGRAM 7. 



the true nourishment of the worm. It would soon die if it were 

 obliged to swallow pure sand. 



The Leeches are annelides which have suckers at both extremi- 

 ties of their body to fix themselves ; in the middle of the front 

 sucker is the mouth. Leeches live in stagnant water. They were 

 formerly very much used in medicine, but are now employed much 

 less frequently. They live only on blood. Old horses are driven 

 into the marshes where they breed, and the leeches attach them- 

 selves to their legs. Their mouth is furnished with three hard 

 projections, bearing small sawlike teeth. The leech makes the 

 wound from which it draws blood by making these three projections 

 act on the spot where it is fixed by its sucker. The scars which 

 succeed these wounds are therefore always triangular. The leech 

 gorges itself with blood till it can scarcely move ; but it requires a 

 considerable time to digest this large quantity of food. It can be 

 made to vomit up by laying on it a pinch of salt or tobacco, or 

 even sugar, which is a poison to some animals. 



