204 
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 cesophageal 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 cheetigerous segments (19 and 17), 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 Arveni1c¢o lime 
The discussion of the affinities of the Arenicolide 1s 
rendered somewhat difficult owing to the fact that the 
details of the anatomy of one or two of the neighbouring 
families are very unperfectly known. The three families 
Arenicolide, Scalibregmide, and Ophelide have several 
features in common, as they are limnivorous and present 
certain of the peculiarities characteristic of such Poly- 
cheeta. 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 cesophagus (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 
