26 OUTLINES OF NATURAL HISTORY. 



tlie edges of wliich are serrated with numerous minute 

 teeth. These three jaws are so disposed as to meet in a 

 single point, in a triradiate manner, and they are the 

 organs by which the Leech cuts through the skin, in order 

 to get at the blood-vessels beneath. Hence the bite of a 

 leech consists of three little cuts radiating from a point. 



The mouth opens by a short gullet into an alimentary 

 canal, the first portion of which, usually termed the 

 "stomach," occupies nearly the whole of the body-cavity, 

 and is furnished with eleven membranous pouches on each 

 side. The pouched "stomach" has the function of separ- 

 ating the watery part of the blood which the animal takes 

 as food ; and it opens into an intestine which terminates 

 at a distinct vent placed on the back a little in front of 

 the hinder sucker. 



There is no distinct heart, and the place of the blood- 

 vessels is taken by a peculiar system of tubes, containing 

 a fluid which appears to play the same part in the economy 

 of the animal as does the true blood of higher organisms. 



It is doubtful, also, if there are any definite breathing- 

 organs ] but the animal is furnished with a series of little 

 pouches (fig. II, B, r r) which are placed on each side 

 of the body, and have commonly been called " respiratory 

 sacs." There are seventeen of these little organs on each 

 side of the body, and they open on the lower surface by 

 a series of minute pores. 



The nervous system has the form of a chain of little 

 nervous masses (fig. ii. A, n n) placed along the lower 

 surface of the body, and united lengthways by cords. 

 The first of these masses, representing the brain, is placed 

 above the gullet, which is thus embraced by the cords 

 which unite this with the next nervous mass in the series. 

 The top of the head (fig. n. A, h) also carries ten eyes, 

 disposed in the shape of a horse-shoe. 



The Leech attains a length of from two to three inches ; 

 its back is olive-green with rusty-red longitudinal stripes, 

 and its lower surface is greenish-yellow spotted with black. 

 In the nearly-allied Sanguisuga medicinalis, the lower 

 surface of the body is olive-green, and is not spotted. 



