BRITISH ANNELIDS. 239 



sent only one species of Allunis (subject to variation, liowever, as \vc 

 shall see later on), it will be utterly impossible to confound it with 

 AllolobopJiora when we have once seen and examined it. We are 

 thus narrowed down practically to the two genera I.umbi-iciis and 

 Allolohophora^ and have, as external guides to their distinction, the 

 mode of insertion between lip and peristomium, the colour, and the 

 setje. Since the latter are variable we may be obliged occasionally 

 to resort to anatomy before we can be absolutely certain about a 

 given species ; but I believe that I shall be able to show as we pro- 

 ceed that all the species may be readily distinguished by external 

 characters alone, if only they are mature. I shall endeavour to give 

 such unmistakable clues to the identification of each species by 

 external means as shall render the use of the knife and the micro- 

 scope unnecessary. 



Those who have followed me thus far will have learned which 

 are the leading portions of the bocy of a worm, and what parts must 

 be particularly observed in order to obtain a clue to their identity. 

 I may add now a few more details which will be helpful, and explain 

 some terms which will be constantly met with in the study of 

 Annelid literature. 



Beginning with the front or anterior portion of the body we find 

 that there is no distinct head, while no organs of vision or hearing 

 are anywhere apparent. 'J'here is a retractile lip, usually called the 

 prostomium on account of its being in front of ai.d above the mouth 

 (stoma). The first ring, segment, or somite, bears no setae or 

 bristles, and is called the peristomium, because it surrounds the 

 mouth. Some works include this ring in all calculations relating to 

 the number of segments, but it is usual in England to omit it, and 

 begin to reckon from the first segment which carries bristles. The 

 setae are organs of locomotion. Along the back, in the groove between 

 each segment, one will be able to discover a series of pores oi 

 punctures which look as though a pin had been thrust through th( 

 skin. These are the dorsal pores of which an account w ill be found 

 in "Science Gossip," December, 1891. The male pore, found on 

 segment fifteen, except in the case of A/lurus, is to be looked 

 for on the lower surface of the body. In some species the opening 

 is seated on a cushion or papilla of very delicate structure, which 

 gives it great prominence ; but in other cases only a well-trained eye 

 will detect it. The Greenworm and the Common Earthworm have 

 the most prominent papilla for the male pore, and these should be 



