DISTRIBUTION OF BRITISH ANNELIDS. 143 



while the tubercula form a band on the four innermost of the 



29 — 37 



girdle segments. On the other hand, the symbol ^^^ . ^^ . g^ 



would show that, while the girdle occupied the 29th to the 37th 

 segments, the tubercula do not form a continuous band, but 

 consist of pores on alternate segments. 



Our earthworms were formerly arranged under three genera : 

 Lumbricus, Allolohophora, and Allurus. When the internal 

 structure came to be studied, however, it was found that the 

 large genus Allolohophora included such a heterogeneous assem- 

 blage that further division was necessary. I shall be content 

 with the briefest possible notes on these matters, as these papers 

 are not intended for a systematic study of worms, but as a guide 

 to the knowledge of their distribution. 



I. Lumbricus. 

 Beginning with the oldest, best known, and most widely 

 distributed group, we find that there are five true species of 

 Lumbricus at present known in the British Isles. Judging from 

 certain facts we ought to find three other species, but so far, 

 if they exist, they have eluded our search. This group is known 

 by the colour, which is more or less purple and iridescent, but, 

 as this character is also found among the Dendrobcenas, it is 

 well to notice the fact that the head is inserted into the first 

 segment (or peristomium) by means of a backward growth which 

 extends to the intersegmental groove. In other words, the 

 prostomium entirely divides the peristomium, while the setas 

 are always strictly paired. The male pores are on the 15th 

 segment, with or without papillae, the tail is usually flattened, 

 and the girdle covers six segments (except in L. papillosus), 

 while the tubercula form a band on the innermost four. 



32 — 37 



1. Lumbricus terrestris, L. gg^g The Common Earthworm. 



29 — 32 



2. L. rubellus, Hoff. o^ _ ■., The Eedworm, smaller than the 



last. 



g 



exactly like the last, but with papillae on segment 15. 



4. L. papillosus, Fri< 

 Closely resembles No. 1. 



3. L.festivus, Sav. {= L. rubescens, Friend), ^^^^q Almost 



4. L. papillosus, Friend (= L.friendi, Cognetti). 3^,3^ 



