88 P. W. GAMBLE, M.SC, AND J. H. ASHWORTH, B.SC. 



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 

 occiirrence on the north coast of Alaska (Murdoch 1 ), 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, differing 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 pro- 

 truded when the tide comes in. The size and coloxir 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 provided with three to five pairs of short lateral twigs 

 (PL VI., Fig. 3). The proboscis and prostomium are only slightly 

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



Where, however, the amount of oi'ganic matter is consider- 

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

 prostomium, proboscis, gills, and epidermis are black. The gills are 

 better developed than those of worms living in purer sand. These 

 differences are probably due to more abundant nutrition. The time 

 of maturity of both these forms of the littoral variety on the Lancashire 

 coast is the summer, while at St. Andrews they are found mature from 

 February to September. 



(2) The second variety occurs on the Lancashire coast at the upper 



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



