WOEMS. 207 



joint may be regarded as an individual animal. The 

 joints of other segmented worms (earthworms) do 

 not become detached, like those of tapeworms, for 

 the purpose of reproduction. The nervous system is 

 absent in the lowest worms; in the higher worms 

 ganglia always constitute its central parts, and in 

 annelids these are arranged in pairs on the ventral 

 side of the body, and united by nerve fibres into a 

 ventral cord, which is connected in front with a 

 nerve-ring surrounding the gut and thickened above 

 into cerebral ganglia. In many worms {e.g. tape- 

 worms and flukes) the nervous system is of much 

 simpler structure. The sub-kingdom of worms con- 

 tains a very large number of forms. It is only 

 necessary to mention here representatives of three 

 classes : Segmented worms {Annelida), round worms 

 {Nematelminthes), and flat worms {Platyelminthes). 



CLASS : ANNELIDA (SEGMENTED WOEMS). 



Segmented worms with rounded (earthworm) or 

 flattened (leech) bodies, and possessing both mouth 

 and anus. They fall into two sub- classes : I. Leeches 

 {Biscophora), II. Bristle-worms {ChcRtopoda). The 

 first possess suckers as organs assisting locomotion, 

 the latter foot-stumps, which bear longer or shorter 

 bristles ; but these foot-stumps may be absent, and 

 the bundles of bristles are then simply imbedded in 

 pits. The latter is the case in the only members of 

 the class which interest us here, i.e. the earthworms. 



The Earthworms {Lumbricus). 



There are several species in the genus, but all agree 

 in their habits. The body of the earthworm is slender 

 and cylindrical, tapering in front and somewhat 

 flattened behind. On the ventral side of the second 

 segment is found the opening of the mouth. There 



