156 INSECTS ANNELIDA DIAGRAM 7 



the true nourishment of the woim. 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 t of the front 

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

 were formerly very much used in medicine ; but are now em- 

 ployed much less frequently. They live only on blood. Old 

 horses are driven into the marshes where they breed, and the 

 leeches attach themselves 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. 



