FEEDING OF CREPIDULA. 451 



lateral cilia are by far the stronger, just as one would expect to find, 

 seeing that they have to draw a current of water through the mantle 

 cavity, while the other rows merely pass on the food-particles. 



The ventral rows of cilia lash in a direction from left to right, and, as 

 has already been remarked, are the main collectors of the fine food- 

 particles. The dorsal rows of cilia lash in the same direction as the 

 ventral rows, but on the opposite face of the gill; whatever particles 

 are passed on to them by the lashings of the lateral cilia they wash 

 along the dorsal face of the filament, through a notch in the tip of the 

 latter (see Fig. 3), and round to the large cilia on the ventral surface 

 (see Fig. 6). The dorsal cilia, however, also assist in maintaining the 

 food-current, and in modifying the direction of the current formed by 

 the " lateral " cilia, for a glance again at Fig. 6 will show that the re- 

 sultant direction of the water current produced by all the cilia on the 

 gill is in a direction opposite to that in which the free filament swims. 

 Thus, in the living animal the effect of the dorsal cilia on the current 

 on its passing through the gills is to turn it towards the right, namely, 

 towards the exhalent aperture (see Figs. 7 and 8). The groups of large 

 cilia on the ventral tips of the filaments are probably the chief agents 

 in pushing the collected food forwards towards the mouth, being 

 assisted in this by the cilia in the food-groove. The tips of the fila- 

 ments are covered all over with cilia ; those on the anterior and posterior 

 faces doubtless assist in interlocking the filaments. 



In connection with the gill-filaments, there still remains to be con- 

 sidered the action of those cilia which occur on the floor of the posterior 

 part of the mantle cavity, that is, on that part of the mantle lin- 

 ing the dorsal surface of the visceral mass. In this region the 

 cilia wash particles from left to right into a ciliated path on the right 

 side, which path is continuous with the food-groove (see Fig. 2, B) in the 

 anterior region. The mantle to the right of the ciliated path bears 

 cilia which lash particles into the same path, working however in 

 a direction mainly dorso-ventral. 



The cause of the forwardly-directed current at the anterior end of 

 the inhalent chamber is found in the presence of strong and active 

 cilia on the lips of the food-pouch, on the inner side of the mantle, and 

 especially those on the dorsal surface of the left epipodiurn. The food 

 which is washed forwards by these groups of cilia is directed into the 

 food-pouch chiefly by the cilia on the dorsal lip of the latter, but it is 

 pushed along inside the pouch by cilia, being assisted in this, however, 

 by slow, wave-like pulsations of the side-walls. In the capture of 

 food-particles there is no doubt that the secretion of mucus for 

 ■entrapping the particles is a very important factor, and a more correct 



