FEEDING OF CEEPIDULA. • 471 



forwardly directed stream in the inhalent chamber in Crepidula is 

 equivalent to that caused by the ciliated path on the mantle of 

 Lamellibranchs ; the purpose of the stream in both animals being 

 that of expelling undesirable material from the inhalent chamber. 

 There is this difference, however, that Crepidula, unlike the oyster, 

 has the option of ingesting the automatically selected heavier par- 

 ticles. On the other hand, in the oyster and other Lamellibranchs 

 the fringes of tentacles on the edge of the mantle form a coarse sieve 

 by interlacing at the entrance to the mantle cavity, and in this way 

 prevent the entrance of coarse particles ; it is possible, however, that 

 the particles collected on the mantle in Lamellibranchs might' be 

 picked up by the gill and conveyed to the mouth, as probably happens 

 in the posterior region of the inhalent chamber of the oyster and the 

 scallop. Both animals have still another opportunity for selecting 

 their food-material, namely, by refusing the food-masses which are 

 brought by the gills to the mouth. It has been observed that both 

 animals do at times refuse such food, so that selection of food-material 

 is undoubtedly exercised in this way. From my preparations of the 

 gut contents of these two animals, I received the impression that 

 those of the oyster were the finer, but as I have examined compara- 

 tively few specimens, it is doubtful whether that observation has any 

 significance. It w^ould be necessary to examine and compare a larger 

 number of individuals to obtain a significant result. The fine food- 

 particles are collected on the gill in both Crepidula and Lamelli- 

 branchs, and conveyed along food-grooves to the mouth, but Crepidula 

 may be regarded as having gained an advantage over Lamellibranchs 

 by closing in its food-groove, and thus ensuring the capture of the 

 food. If disturbed while feeding an oyster would be much more liable 

 to lose its food than Crepidula. 



There is, however, an interesting difterence in the position of the 

 lateral cilia on the filaments in Crepidula and Lamelhbranchs. In 

 Crepidula these cilia are nearer the exhalent chamber (see Fip-. 6, I.e., 

 p. 452), while in Lamellibranchs they are nearer the inhalent chamber 

 (see Fig. 18, I.e., p. 468). An explanation of these phenomena will 

 probably be offered when more Gastropod gills have been studied. 



It will now be apparent how remarkably similar Crepidula, its 

 allies, and Lamellibranchs are in the details of their modes of feed- 

 ing. The closeness of the resemblances they offer may fairly be 

 regarded as an expression of the similar tendencies they have derived 

 from their common origin. 



