G4 Arenicolidae 



is accomplished by repetition of the following operations : the 

 " proboscis " is extended, pressed into the sand, and withdrawn full 

 of sand, which is passed backward into the oesophagus. The body 

 is thrust forwards, partly by the action of the longitudinal muscles 

 and partly by the peristaltic waves produced by the successive con- 

 tractions of the circular muscles of the body. By the latter means, . 

 which causes surging forwards of the coelomic fluid, the anterior end is 

 rendered tense, and, in the caudate species, especially in A. marina, 

 becomes dilated, and is thus able to enlarge the depression which has 

 been made in the sand. The passage, which is made partly by the 

 sand being swallowed, partly by its being forced aside, is smoothed 

 by contact with the tense anterior segments, and may be lined with 

 mucus secreted by the epidermis of the anterior region.^ The first 

 few segments are thus of chief importance in burrowing operations ; 

 the branchial region, being in most examples of the caudate species 

 narrower than that which precedes it, is therefore less subject to 

 friction, and in all species the notopodial chaetae are capable, when 

 extended fan-wise, of affording the gills some protection against 

 undue friction. The branchial region of the animal is more or less 

 passively drawn forwards, after each onward thrust of the anterior 

 region, as the animal progresses in its burrow ; meantime, the waves 

 of contraction pass regularly forwards from segment to segment, and 

 serve the double purpose of rendering the anterior region turgid and 

 of assisting respiration by agitating the water in the burrow, thus 

 causing a change of water around the gills. These waves are, of 

 course, best seen in the aseptate region of the body. After 

 burrowing more or less vertically downwards, to a depth of from one 

 to tw^o feet, the littoral form of A. marina may make a horizontal or 

 oblique passage, and then a second vertical one which opens at the 

 surface of the sand in a small funnel-shaped aperture. This funnel- 

 like aperture is said by M. Bohn to be due to the subsidence of the 

 sand at the surface brought about through the removal of the subjacent 

 sand, during feeding, by the proboscis. M. Bohn believes that from 

 the vertical shaft of the burrow one or more horizontal galleries are 

 formed, but that they have no communication with the exterior. 

 This is undoubtedly sometimes the case, as the writer can corro-- 

 borate, for, while digging for small specimens about mid-way between 

 tide-marks, he has exposed them in L-shaped burrows. The blind 



' The sand in contact with the burrow often exhibits a reddish or brownish 

 discolouration, due to some chemical change induced in the iron -containing 

 constituents. 



