X] HIRUDINEA 165 



ponds it inhabits. Clepsine, one of the Rhynchobdellidae which 

 is very common in Britain, attaches its eggs to some stone or water- 

 plant, or in some species carries them about on its ventral surface. 

 It has developed a quite maternal habit of brooding over the eggs, 

 and when the young are hatched it carries them about and they 

 feed oh some secretion from its body. 



Of the Gnathobdellidae, Hirudo medicinalis is found in Great 



Britain, but is commoner in some parts of the Con- 

 Habits, etc. . _ . . 



tinent. It is cultivated in some districts, but the 



demand for it is decreasing with the disappearance of blood- 

 letting. It becomes mature in three years. In the young stages 

 it sucks the juices of insects. Another common but small 

 Gnathobdellid leech is the brownish Nephelis, which frequents our 

 ponds and pools ; it feeds on snails and planarians. A large species 

 of the same genus is common in the shallows of the St Lawrence, in 

 Canada. In warmer climates many leeches take to living on land, 

 and are a source of great annoyance to travellers whose blood they 

 suck. Even water-forms do much damage unless carefully guarded 

 against. Certain .species make their way with drinking water into 

 the throat and back of the mouth, on which they fasten, and so 

 cause great suffering both to man and cattle. 



Phylum ANNELIDA. 



This phylum includes segmented animals with, as a rule, a well- 

 developed coelorn and metamerically repeated nephridia. The 

 cuticle is always thin and flexible, and the nervous system consists 

 of a pair of supra-oesophageal ganglia, a nerve collar and a ventral 

 nerve-cord which has a ganglionic swelling in each segment. 



Class I. CHAETOPODA. 



Annelida which possess bristles (chaetae) embedded in pits in 

 the skin and serving as organs of locomotion, or which are believed 

 to have once possessed such organs and to have lost them. 

 Order 1. Oligochaeta. 



Chaetopoda which have the chaetae arranged singly or in 

 pairs and which have neither parapodia nor tentacles : the 

 generative organs are definitely localised and the sexes are 

 united in the same individual : development is practically 

 entirely embryonic : the group inhabits fresh water or damp 

 earth. 

 Ex. Lumbricus, Allolobophora. 



