FEEDING OF CREPIDULA. 473 



Purpura, Nassa, Buccinuin — in all these — the gill-filaments are ciliated 

 in essentially the same way as those of Crepidula. There are generally 

 present lateral, frontal andab-f rental cilia, and the gill-filanients,or rather 

 gill-leaflets, closely resemble those of the Protobranchs. The lateral 

 cilia in all the forms examined prodvice the main current in the mantle 

 cavity. The occurrence of frontal and ab-frontal cilia in all these 

 forms is a matter of much interest. In all cases these cilia collect 

 plankton from the ingoing current, but whether such collected food is 

 eaten I am not yet able to say. It seems probable that all these forms 

 may be found to feed partly on plankton. A research into this matter 

 is being made. In some cases (namely, Fissurella and Buccinum) the 

 gill undoubtedly divides the mantle cavity into inhalent and exhalent 

 chambers as occurs in Crepidula and its allies. At the tips of the fila- 

 ments in all these forms there are interlocking cilia similar to those at 

 the tips of the gill-leaflets of Nucula. These cilia doubtless serve to 

 effect a junction between the gill and the opposite wall of the mantle. 

 Thus there can be no doubt that most Gastropods on further investi- 

 gation will be shown to have the mantle cavity divided by the gill 

 into two chambers. 



A point of some interest presents itself at once on comparing the 

 gill-filaments or gill-leaflets of the Aspidobranchs and many Pectini- 

 branchs with the gill-filaments of Crepidula and Calyptraea, namely, 

 that the gill-leaflets of the former bear the same relation to the 

 filaments of the latter that the gill-leaflets of Nucula bear to the gill- 

 filaments of the Filibranchs. Thus the Pectinibranchs already present 

 the same range of gill-features that I propose should be united in the 

 Filibranchiate Lamellibranchs. It may here be remarked that the 

 similarity in the structure and function of the gills in Gastropods and 

 Lamellibranchs shown by the foregoing observations, emphasizes that 

 close relationship between these groups, which Pelseneer has already 

 pointed out (17). 



A cursory examination of the gills of Chitons indicates that rows of 

 lateral cilia on the gill-leaflets produce the main current through the 

 mantle cavity in a manner similar to that in Gastropods and Lamelli- 

 branchs. 



XV. SIGNIFICANCE OF CHAIN FORMATION IN THE MODE 

 OF FEEDING OF CREPIDULA. 



It is well known that Crepidula has the curious habit of forming long 

 chains by one individual settling on the back of another; as many as 

 fourteen individuals may l)e found holding together in such a manner, 

 and usually there is a gradation in size from the largest at the bottom 



NEW SBRIEiS. — VOL. IX. NO. 3. JUNE, 1912. 2 H 



