158 
proboscis is protruded, pressed into the sand and with- 
drawn full of sand and again everted. The body is thrust 
forward partly by the action of the longitudinal muscles 
of the body wall, and partly by the peristaltic waves pro- 
duced by the circular muscles, by means of which the 
anterior end is also rendered swollen and tense, and is 
thus enabled to enlarge the burrow. By these means a 
passage is eaten and forced through the sand, smoothed 
by contact with the skin, and may be lined with mucus 
secreted by the epidermis. The gill region, being 
narrower than that which precedes it, is to some extent 
protected from friction, and the notopodial sete are also 
directed so as to protect the gills. After burrowing 
vertically downwards to a depth of from one to two feet, 
the littoral forms may make a horizontal or oblique 
gallery, and then a second vertical one, which opens on 
the surface of the sand in a small funnel-shaped aperture.* . 
The burrows of Laminarian worms, and those of some 
littoral specimens, are simple vertical excavations (not 
U-shaped), in which the animal is almost invariably 
found head downwards.t 
The amount of work done by Arenicola has been 
estimated by Davisont on the Holy Island Sands. As 
the result of observations upon the number and weight of 
** G@. Bohn (‘‘ Observations Biologiques sur les Arénicoles,’’ Bulletin 
du Muséum d’histoire naturelle, 1903, No. 2, p. 62) states that the 
burrow of the littoral form is not U-shaped, and that it does not open 
at the funnel-shaped aperture. He believes that the latter is due to 
subsidence of the surface sand brought about by the subjacent sand 
being removed during feeding by the proboscis of the worm. All other 
observers agree that the burrows are, in the majority of cases, 
U-shaped. 
+ For an account of curious seasonal changes in Arenicola and 
other burrowing marine animals see G. Bohn, ‘‘ Les intoxications 
marines et la vie fouisseuse,’’ Comptes Rendus de ]’Academie des 
Sciences, Paris, tome 133, pp. 593-596; and ‘‘ L’histolyse saisonnieére,”’ 
ibid. pp. 646-648. 
} Geological Magazine, vol. viii., 1891, p. 489. 
