4 r. W. GAMBLE AND J. H. ASH WORTH, 



attacks of enemies,^ and in such cases there is an approxima- 

 tion to the type of gill seen in the littoral variety, though a 

 certain amount of difference is always observable. 



Thus there appear to be two varieties of the common 

 lugworm on the Lancashire coast, distinguished by their 

 habits, external features, and periods of maturity, but there 

 are no important structural points of difference. 



The habits of Arenicola marina at the breeding season 

 are still to a large extent unknown, and developing eggs have 

 not hitherto been obtained. It has been stated that, when 

 mature, the animal is in the habit of swimming freely (Ehlers, 

 1892, «), but we are unable to confirm this. The post-larval 

 stage, however, appears to be, for a short time, pelagic (Benham, 

 1893) . 



The curved burrow of the shore lugworm is formed by the 

 combined action of the proboscis, the swollen anterior region 

 of the body, and the waves of muscular contraction which pass 

 along the body from behind forwards. When the proboscis is 

 everted and pressed into the sand, the prostomium is slightly 

 retracted into the body. The proboscis is withdrawn full of 

 sand, again everted, and the body is thrust forward, partly by 

 contraction of the longitudinal muscles, partly by a peristaltic 

 wave produced by the circular ones. The anterior end is in 

 this way rendered swollen and tense, and is able to enlarge the 

 burrow, and thus a passage is gradually eaten through the sand, 

 smoothened by contact with the skin, and lined by the mucous 

 secretion of the epidermis. The gill region being narrower 

 than that which precedes it, is thus, to a certain extent, pro- 

 tected from friction, while, as if to ensure this, the notopodial 

 pencils of bristles are directed so as to protect the gills. After 

 burrowing vertically downwards for a depth of from one to 

 two feet, the worm forms a horizontal or oblique gallery, and 

 then a second vertical one which ends at the "countersunk" 

 hole, through which the anterior part of the worm may pro- 

 trude, and so bathe the gills in fresh sea water. 



^ Seethe curious account of tlie ravages of Corophium lougicorne, 

 by d'Orbigny, 'Journal de Physique,' 1821. 



