LEECHES. CLASS OF ENTOZOA. 309 



be extremely imperfect. The greater number of the Leech tribe 

 are inhabitants of fresh water ; some, however, are only found 

 in the sea ; others live in moist situations near stagnant water, 

 pursuing Earth- Worms, &c. ; and there is one small species, 

 entirely terrestrial, which inhabits the woods of Ceylon, and 

 attacks men and horses that are passing through them, in such 

 a manner as to become, from its great voracity, one of the most 

 troublesome pests of that fine island. The species of the genus 

 Cfepsine, which inhabit fresh waters, suck the blood of the com- 

 mon Pond-snails. Most of the marine species are parasitic in 

 their habits ; the Malacobdellce attaching themselves to bivalve 

 Mollusca, whilst others infest fishes, and one, the Udonella call- 

 gorum, feasts upon the juices of a small Caligus(^ 889), which is 

 itself parasitic upon the liolibut. 



CLASS OF ENTOZOA. 



920. This class derives its nan e from the peculiar mode of 

 existence of the animals composing it ; most of them being 

 inhabitants, during their whole lives, of the bodies of other 

 animals, generally of higher organisation, from the juices of 

 which they derive their nourishment. Many of these possess a 

 distinct worm-like form ; the body being much prolonged and 

 exhibiting a slight indication of a division into segments, and 

 the mouth being situated at one extremity. These, therefore, 

 evidently belong to the Articulated series. There are others, 

 however, which, in their general form and the simplicity of their 

 organisation, seem scarcely to agree with the Articulate type of 

 structure. 



921. There is a very interesting group, consisting of the 

 genus Planaria and its allies ; which is placed in this class on 

 account of its general conformity with it in structure; although 

 not agreeing as to the residence of the animals composing it, 

 ihese not being inhabitants of the bodies of other animals, 

 but swimming freely in waters of the ocean, as well as in 



VOL. n. z 



