210 



THE MECHANISM OF FEEDING 



As will later he shown, a considerable portion of the nourishment of Teredo is 

 derived from the wood in which it bores. But a part of its food is undoubtedly made 

 up of plankton organisms, which are being continually taken in with the respiratory 

 current. 



A somewhat detailed account of the ciliary mechanism for the capture and 

 transportation of food in Mya, the soft-shelled clam, has been given by Yonge 

 (1923). No such investigation has been made in the case of Teredo, but a few prelimi- 

 nary observations indicate that a similar apparatus is present. Foreign particles 

 touching any part of the body wall, mantle, or gills are immediately entangled in 

 mucus secreted by the epithelium. Anything falling on the gills is quickly carried 

 by cilia to the nearest branchial groo\'e, the cilia of which bear material rapidly 

 forward to the region of the mouth. 



The dorsal and ventral lips of the mouth are continuous, respectively, with a 

 pair of dorsal and a pair of ^•entral labial palps. The dorsal palps in Teredo navalis 

 are small and inconspicuous, but quite distinct (fig. 76), while the ventral ones are 

 reduced to slightly raised, ciliated patches on the sides of the foot. The under sides 

 of the dorsal palps are also ciliated. The labial palps of other lamellibranchs are a part 

 of the mechanism for bringing plankton food to the mouth, and this function is doubt- 

 less retained in Teredo. 



In Bankia setacea the labial palps, both dorsal and ventral, are rather well de- 

 veloped. Deshayes (1848) and Quatrefages (1849) figured two pairs of long, narrow' 

 palps in species studied by them. It appears evident that these structures will, in 

 some cases at least, be of value in systematic distinctions. 



Teredo is unlike the more generalized lamellibranchs in that cilia do not cover 

 the visceral sac and the interior of the mantle, but are restricted to a narrow strip on 

 the mantle opposite the branchial groove. These cilia beat in such a way that particles 

 entangled in mucus are borne rapidly toward the posterior end of the infrabranchial 

 cavity. If the branchial groove is carrying forward more than a very small amount 

 of material, it is, without doubt, caught away and carried back by these cilia. Thus 

 we have a mechanism which determines, on the basis of quantity, not of quality, 

 whether or not matter taken from the water shall reach the mouth. 



Particles falling on the non-ciliated surface of the mantle or body are drawn into a 

 ciliary current by the strands of mucus that are secreted. Material that is carried 

 posteriorly by the cilia on the mantle collects in the posterior part of the infrabranchial 

 cavity, and is expelled at intervals through the incurrent siphon, apparently by a 

 quick contraction of the mantle. This corresponds to the action of other moUusks 

 with a closed mantle as described by Kellogg (1915), except that there the adductor 

 muscles effect the contraction. The details of the ciliary mechanism of Teredo remain 

 to be worked out, l)ut it is apparent that there exists an apparatus similar to that of 

 other lamellibranchs for the capture and transportation of plankton. 



THE DIGESTIVE TRACT 



The mouih of Teredo, as in most bivalves, is a small, median, transverse slit, 

 dorsal to the foot. The oesophagus is short, dorso-ventrally compressed, and heavily 

 ciliated throughout its length. It narrows posteriorly, so that its width at the stomach 

 is about one-half that at the mouth. In the walls are several longitudinal furrows. 



The stomach (figs. 77 and 78) is long and subcylindrical. Most of the digestive 

 glands lie on the right side of the visceral mass, so that the stomach lies somewhat to 



