130 
INTRODUCTION. 
Arenicola* is a genus of abundant and _ widely- 
ranging Polychet worms, represented in the British 
fauna by three species,t all of which may be found 
between tide marks in the neighbourhood of Port Erin 
(Isle of Man) and Plymouth. 
The common lugworm, Arenicola marina, forms a 
convenient type of the genus. It is abundant on most of 
the sandy shores around the British Isles. Its presence 
is indicated by the small heaps or coiled castings of sand, 
which are familiar objects between tide marks. The 
animal may be found on digging to a depth of one to 
three feet near such castings, and it is commonly so 
obtained by fishermen, by whom it is extensively used as 
bait.- Its general appearance may be seen in Fig. 1. It 
is almost invariably slightly inflated in the anterior 
region, being widest at a point about one-sixth of its 
length from the anterior end. 
Hapirs, VARIETIES. 
There are on the Lancashire coast and in the Firth of 
Forth, two varieties of A. marina which differ in habits 
and in two structural points. 
* While the following account owes much to the memoir published 
in 1898 by Dr. F. W. Gamble and myself (Quarterly Journal of 
Microscopical Science, Vol. 41) it should be said that a large portion 
of it is new, consisting of observations on the development and post- 
larval stages and of new points relating to some of the systems of 
organs. All the statements from the earlier memoir used in the 
present one have been carefully revised and some of them corrected in 
the light of further investigations I have made on the genus during 
the last six years. 
+ A. marina, Linneus; A. grubw, Claparéde; <A. ecaudata, 
Johnston. 
+ T have added a section (see p. 219) dealing with some points of 
economic importance, such as its abundance in various sands, its 
efficacy as compared with that of other bait, etc. 
