BRITISH ANNELIDS. 



109 



With this systematic arrangsmcnt of the genus before us, it will 

 now be necessary to inquire how the various species of Allolobophora 

 maybe differentiated. To render this point more easy I have arranged 

 the genus in natural groups, depending upon a number of clearly 

 defined characteristics. All the species at present known to science 

 fall under some four natural heading ; but as one of these groups is 

 represented in Great Britain by only one solitary species at present, 

 I shall limit the group to three. ^ These I will again arrange in a 

 systematic way in order to show their principal characteristics at a 

 glance. 



Tabular View of the Genus Allolobophora. 



§ I. Lumbricoidea. 



Large, closely resem- 

 bling- /Aimbricus ; usually 

 dark in colour, with setae 

 in close couples ; cylin- 

 drical in front, flattened 

 behind. First dorsal pore 

 usuall}' about the nth or 

 I2th segment. Exude a 

 slimy substance, but no 

 coloured mucus. Found 

 usually in rich soil, ara- 

 ble or pasture, or among 

 manure. Usually addicted 

 to burrowing and making 

 large worm-casts on the 

 surface of the soil. 



§ 2. Mucida. 



Medium, not resembling 

 Lumhricus ; colour very 

 variable, with set£e in close 

 couples ; usually more or 

 less cylindrical throughout. 

 First dorsal pore usually 

 about the 4th or 5th seg- 

 ment. Exude a coloured 

 and more or less abundant 

 mucus, sometimes very 

 foetid. Found largely 

 under stones and among 

 vegetable debris. Not 

 usually addicted to bur- 

 rowing or making worm- 

 casts on the surface of the 

 soil. 



§ 3. Dendrobsena. 



Small, often not more 

 than an ii.ch long. Rose- 

 red or dark brown in 

 colour. Setoe usually wide 

 apart ; body more or less 

 angular behind. First 

 dorsal pore usually about 

 the 5th or 6th segment. 

 Exude a slimy substance, 

 but sometimes a coloured 

 mucus as well. Found 

 under the bark of decay- 

 ing trees, and among rot- 

 ling timber, or decaying 

 vegetable matter. Not 

 addicted to making worm- 

 casts except under fallen 

 trees or in woods. 



It is but right to state that each of these groups runs into the 

 other, so that there is no hard and fast line to be drawn between 

 them ; just as we cannot absolutely differentiate the genus Ltimbrims 

 from Allolobophora so as to include every species known to science. 

 Every system breaks down if pressed too hard, and even among 

 the earthworms we find that Nature makes no freaksome leaps, but 

 progresses on regular lines. 



I purpose now taking the three groups of worms belonging to 



I Since this article was written I have not only added to the list of British Worms, but 

 have also seen Rosa's excellent arrangement. On the strength of these, it will be necessary 

 eventually to modify the propoted plan somewhat ; but, for the present, I allow my arrangement 

 to stand unaltered. 



