2 F. W. GAMBLE AND J. H. ASHWORTH. 



(Verrill, 1881). On both sides of the Atlantic, latitude 40° N. 

 marks approximately the southern limit of Arenicola 

 marina. South of this it is replaced in the Mediterranean 

 by A. Claparedii; Lev., and by A. cristata, Stimps., the 

 latter also ranging on the west side of the Atlantic from Cape 

 May (N. J.) to the Caribbean Sea. Its reputed occurrence on 

 the north coast of Alaska (Murdoch^), at Vancouver Island 

 (Marenzeller, 1887), Coquimbo, and South Africa requires 

 confirmation. 



An abundant, widely ranging, and undoubtedly old form 

 such as Arenicola, might be expected to vary considerably 

 in its habits and structure, though it has not hitherto been 

 ascertained how far this is the case. Having paid special 

 attention to this point, we have found that there are (at least 

 on the Lancashire coast) two varieties of A. marina, differ- 

 ing in habits, structure, and times of maturity, and that there 

 is, in addition, considerable individual variability. 



(1) From high- water mark down to the beginning of the 

 Laminarian zone, the common shore lugworms (or "lugs," as 

 fishermen call them, in contradistinction to the second variety, 

 or " worms ") sink their U-shaped burrows to a depth of from 

 one to two feet below the surface. One end of the burrow is 

 marked by a casting, the other by a " countersunk " hole, 

 through which the head of the lugworm is protruded when 

 the tide comes in. The size and colour of the animal vary 

 with the amount of muddy organic matter in the sand. Where 

 there is comparatively little mud, the Arenicola average 

 about seven inches in length and are somewhat transparent, 

 so that the superficial blood-vessels can be clearly seen through 

 the thin body-wall. The gills, which are not very strongly 

 developed, are composed of nine to eleven branches, each pro- 

 vided with three to five pairs of short lateral twigs (PI. 1, 

 fig. 3). The proboscis and prostomium are only slightly 

 pigmented, and being very vascular, appear red in colour. 



Where, however, the amount of organic matter is consider- 

 able, the worms are usually about ten inches long, and their 

 1 ' Proc. U. S. Nat. Museum,' Washington, vol. vii, 1884, p. 522. 



