132 WILLIAM RAY ALLEN. 



ciliary currents of the inner gills (Figs. I, 2, 4, 6, and 7) are seen 

 to be directed downward. When they reach the lower edge of 

 the gill they pass around the points of the lamella? to the under 

 side. Here the lamellae of the two faces of the gill form an 

 inverted trough (Fig. 7, tr) in which the particles small enough 

 to be used as food may be carried to a point just above the labial 

 palps (Figs, i and 2, A'). At this point they accumulate in 

 strings of mucus until their weight causes them to fall into the 

 mantle chamber, or into the trough formed by the upper margins 

 of the palps. This depends upon the desirability of the material 

 for food, or rather upon the presence or absence of unfavorable 

 stimuli, and is probably regulated by reflexes, since the palps are 

 quite motile, even after being severed. 



The ciliation of the outer gills tends upward (Figs. I and 6). 

 When particles carried upward by their inner surfaces reach the 

 top, they are passed over to the inner gill, and thence to the point 

 described above. But the gleanings obtained by the outer 

 surface of the outer gill pass over to the mantle at the line of 

 their attachment (Figs. I and 6). All material transmitted by 

 the outer gill and collected by the uppermost part of the mantle 

 is removed forward by the latter to a point just above the attach- 

 ment of the palps to the mantle and body wall. So long as the 

 upper edge of the palps remains applied to the mantle this 

 material passes into the trough between the palps, backward 

 around the line of attachment of the two palps, then forward 

 again between them (Figs. 3 and 4). In case of an unfavorable 

 stimulus the palps are withdrawn from the mantle at this point 

 the material glides past them and is carried downward and back- 

 ward by the cilia of the lower part of the mantle to the region of 

 the excurrent siphon (Fig. i). All the cilia of the lower part of 

 the mantle are directed toward the posterior. So are those of 

 the epithelium of the lower body wall. Their function is that 

 of collecting particles to be thrown out. A small portion of the 

 body wall, near the upper margin, is ciliated like the same portion 

 of the mantle, and must be concerned with the collection of food. 



From the foregoing account and from the figures it is evident 

 that the region of the labial palps is the center toward which all 

 the ciliation of the upper part of the mantle chamber tends. All 



