SECT. V. 



LEECHES. 



expanded lip. A nerve-centre below the gullet supplies 

 the lip and jaws with strong nerves. A double longitu- 

 dinal cord, united at equal distances by twenty-one 

 double nerve-centres, extends from a ring 

 round the gullet throughout the whol 

 length of the body, supplies the different 

 organs with nerves, and ends near the 

 vent in a nerve-centre, from whence 

 nerves radiate through the terminal 

 sucker. 



The circulation of the blood and of the 

 colourless liquid, as well as the nerve sys- 

 tem, prevail generally in the Annelids, 

 modified by the structure of the individual. 



The leech, though greedy of blood, lives 

 in fresh- water ponds, wet grass, and damp 

 places, where it never can meet with 

 warm-blooded animals. It probably lives 



on minute aquatic insects. 



The common Earth-worm, which is a 

 principal member of the second order of 

 Annelids, has a more important part as- 

 signed to it in the economy of nature 

 than its humble appearance leads us to 

 suspect. It has a long, soft, cylindrical 

 body tapering to a point at both ends, 

 divided into numerous rings. The mouth 

 is furnished with a short proboscis, or 

 snout, without teeth. A long salivary 

 glandular mass surrounds a short wide 

 gullet, which leads to a digestive organ similar to a 

 gizzard, whence a canal is continued to the vent. The 

 circulation of the two fluids, and the nervous system 

 modified at head and tail, are like those of the leech. 

 Four rows of minute bristles extend longitudinally 

 along the ventral surface of the worm, two on each side. 



Fig. 131. Nervous 

 System of Leech. 



