Food of Arenicola 65 



end of the horizontal limb of each of these burrows, where the head 

 of the worm was found, was somewhat dilated. But in most cases, 

 the burrows, when complete, are U-shaped, one end terminating in 

 the funnel and the other being indicated by the casting. The 

 burrows of the Laminarian form of A. marina are vertical or 

 L-shaped, and the worms in them are invariably found head down- 

 wards. 1 The depth of the burrow of both forms is often such that 

 the anterior region of the worm is situated below the superficial 

 firmer layer of sand, and extends into the subjacent, more or less 

 semi-fluid, mixture of sand and water. 



The food and digestion of Arenicola have been investigated only 

 in A. marina, but no doubt closely similar conditions hold in the 

 other species. The material swallowed consists of sand together 

 with small vegetable organisms, e.g. diatoms, small animals and 

 animal remains ; occasionally a larger animal is swallowed, e.g. Saint- 

 Joseph found in one specimen a partially digested Nereid. This 

 material is passed into the oesophagus, where it is mixed with 

 mucous secretions from the oesophageal cells and, further back, the 

 trypsin-like secretion of the caeca is poured upon it. In the stomach 

 the secretion from mucus-forming and digestive cells is added to 

 the mass. The swinging backwards and forwards of the stomach, 

 brought about by the muscles of the body-wall and by the protrusion 

 and retraction of the proboscis, tends to produce a thorough mixing 

 of the sand and digestive secretions, and thus the latter are brought 

 into contact with the organic substances of various kinds contained 

 in the sand. The soluble products of digestion are absorbed in the 

 sinuses on the stomach by the blood, which passes almost immediately 

 to the hearts, whence.it is pumped into the ventral vessel and thus 

 to all parts of the system. The sand or mud, as passed from the 

 intestine by the anus, forms a rounded or trochoid heap of vermicular 

 coils, along each turn of which a thin cord of mucus may often be 

 seen. These coiled castings of A. marina are familiar objects on 

 innumerable sandy beaches of northern and western Europe, and 

 similar castings are formed by the other caudate species when 

 feeding in not too coarse a medium. 



The burrows of the ecaudate species are oblique or sinuous 

 cavities in the gravel or between the stones and rocks among 

 which these worms live, and the castings, being composed of coarse 



1 Many of the specimens seen in their burrows were found with the anterior 

 and middle parts of the body lying in the horizontal limb, a position doubtless 

 correlated with the greater abundance of water in this region of the burrow. 



F 



