FEEDING OF CREPIDULA. 455 



tend to be dropped out of the current, the lighter particles travel 

 onwards towards the gill. On coming in contact with the gill these 

 particles are either caught by the cilia or in mucus secreted by the 

 gill, and swept by the rows of cilia on the ventral and dorsal faces 

 of the gill-filaments towards the tips of the latter, and deposited in a 

 ciliated groove on the right epipodium, which groove is efficiently 

 roofed in by the flattened tips of the filaments. In the groove the food 

 becomes worked up with mucus into a cylindrical mass which at 

 intervals is passed forwards towards the mouth to be eaten. In the 

 process of eating the food is seized and drawn into the buccal cavity 

 by means of the radula, and there retained by means of the mandibles 

 prior to being swallowed. The heavier food-particles, however, reach 

 the mouth by a difterent route. On falling out of the main stream 

 they are caught in the forwardly directed stream caused by the 

 combined lashings of several groups of cilia, namely, those on the left 

 dorsal region of the animal's " head " and " neck," those on the face of 

 the food-pouch, and those on the left anterior border of the mantle. 

 This stream is directed into the pocket of the food-pouch by the cilia 

 on its dorsal lip where the captured food becomes worked into a pellet 

 and deposited in front of the mouth for eating. If, however, the 

 animal is not wanting food, the entrance to the food-groove is closed, 

 and the stream is directed out of the mantle cavity by way of a 

 ciliated path parallel to the left anterior edge of the mantle. In front, 

 this ciliated path runs parallel with the pocket of the food-pouch (see 

 Fig. 4, B), but behind, it is placed on a fold of skin somewhat similar to 

 that forming the food-pouch. If a large quantity of foreign material 

 be drawn into the mantle cavity, the ciliated path may be formed into 

 a channel by the infolding of the edge of the fold on which the path 

 lies posteriorly, but in front by the raising up of the mantle along the 

 sides of the path. At the same time, the animal shuts off the food- 

 current by closing the mantle cavity, and by covering the gill by the 

 body, confines the intruding material to the forwardly directed stream, 

 and is then able to reject it. Should large bodies get into the mantle 

 cavity, the animal tries very hard to get behind them, and when it does 

 so, pushes the intruding material bodily in front of the lips and 

 extended tentacles out of the apparently sacred precincts of the 

 inhalent chamber into the exhalent chamber, or even right outside the 

 mantle cavity. Intruding air-bubbles have often been seen to give the 

 animals great trouble in this way. In trying to clear the chambers the 

 animal shows some ingenuity in trying difierent plans, but apparently 

 also some stupidity in not widening the exits by raising the shell, and 

 so making its task an easy one. 



