284 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



A. claparedii is at once marked off from the common 

 lugworm and from all other known species of Arenicola by 

 the fact that it has no otocysts. . Other points, such as 

 its well developed lateral prostomial lobes, the presence 

 of several pairs of oesophageal glands, the presence of 

 only five pairs of nephridia and the absence of septal 

 pouches, further separate this species from A. marina. 

 A. marina is also well removed from A. cristata by the 

 number of chsetigerous segments (19 and IT), and gills 

 (13 and 11 pairs), the position of the nephridia (opening 

 on segments 4-9 and on 5-10), and the nature of the 

 otocysts and otoliths. 



Between the two ecaudate species and A. marina there 

 are only the points of agreement which are common to the 

 genus. The common lugworm differs especially from 

 A. ecaudata, and these two species may be regarded as 

 lying almost at the opposite ends of the series. 



The Affinities of the Arenicolidse. 



The discussion of the affinities of the Arenicolidse is 

 rendered somewhat difficult owing to the fact that the 

 details of the anatomy of one or two of the neighbouring 

 families are very imperfectly known. The three families 

 Arenicolidse, Scalibregmida?, and Opheliidse have several 

 features in common, as they are limnivorous and present 

 certain of the peculiarities characteristic of such Poly- 

 chseta. They have a spacious ccelom sub-divided 

 anteriorly by diaphragms and non-septate in the middle 

 of the animal ; the alimentary canal consists of an 

 eversible pharynx followed by an oesophagus (bearing one 

 or more pairs of lateral glandular outgrowths), a dilated 

 stomach and a straight intestine usually with a ventral 

 groove, and the blood-vessels in the middle region of the 



