FEEDING OF CREPIDULA. 



465 



mantle fused ventrally such as the higher Eulamellibranchs, the whole 

 of the ventral region of the mantle lobes may b'e utilized as a settling 

 area from which undesirable material can be removed without 

 interfering unduly with the normal feeding process. 



IX. THE CURRENT-PEODUCING MECHANISM IN 

 LAMELLIBRANCHS. 



With regard to the cause of the main food-current in Lamellibranchs 

 most writers are vague. Herdman and Hornell (10), however, have 

 investigated Margaritifera vulgaris and state cautiously that in 

 this species " the respiratory current is apparently due to the normal 

 rhythmic lashing of the cilia on the large cells at the edges of the fila- 

 ments ; wdiile the collection or the rejection of particles in the water 

 seems to be the result of special action stimulated apparently by the 

 irritation. Particles arrested by the branchial filter are caught up by 

 the nearest cilia, which by local reversed lashing carry them outwards 

 to the free ventral edge of the lamella." 



In Crepidula it is easy to make out with certainty the direction in 

 which the several rows of cilia are working, as the filaments — relative 

 to those of Lamellibranchs — are large. In Nucula, Anomia, Mytilus, 

 Glycimeris, Area, Modiola and Pecten, I also find that it is fairly easy to 

 make out that, as in Crepidula, the lateral cilia which lash across the length 

 of the filaments (see Figs. 15 and 16) are the chief cause of the inhalent 

 current, and that the " frontal " cilia which lash towards the free edge 

 of the gill, collect the food-particles and wash them onwards towards 

 the food-grooves at the edge of the gill (see Figs. 15 and 16). 



Dmcr/mwiv/f/c/fij^rmsic/iAiiAS/f. 



J)/ff£CrmMW.f/C/fFRO//rALC/l//IUS// f^ / Ic Ifc fc 



, ^ O 



9 l^,^j,xx^:ML^i^^J^>^ii^^ 



FOOD ^,^rri^'-% 



FiG. 15.— Lateral view of a living filament of the left outer lamella of the gill of Mytilus 

 cdulis. ( X about 84.) 



I.e. Lateral cilia. l.f.c. Latero-frontal cilia. f.c. Frontal cilia. 



ab.f.c. Ab-frontal or inner cilia. c.d. Ciliated disc. 



A. Arrow indicating roughly the direction in which the latero-frontal cilia lash. 



