466 



J. H. ORTON. 



In Mytilus there are also on the " inner " * or ab-frontal side of the 

 filament cilia which lash in a direction opposite to that of the frontal 

 cilia ; they therefore help in producing the main current as in Crepi- 

 dula. These cilia doubtless also assist in keeping clean the inner 

 surfaces of the gill-filaments. The examination of living filaments of 

 Mytilus revealed inaccuracies in the existing figures of the gill-cilia in 

 this form (see Peck, 14) and Ridewood (13, Fig. 11, c, p. 201). Sections 

 were therefore prepared from well-preserved material, and a drawing 

 of one of these made for Fig. 17 (p. 467). 



FOOD^ 



Fig. 16. — Lateial view of living filament of left outer lamella of gill of Pecten maximus. 

 (x about 130.) 



I.e. Lateral cilia. f.c. Frontal cilia. c.d. Ciliated disc. 



On now comparing the ciliation in Ostrea, Tapes and Cardium,with that 

 in the aforementioned forms, there can remain no doubt that the lateral 

 cilia here also produce the main current by lashing across the length of 

 the filament, while the frontal cilia collect the food-particles by lashing 

 towards the free edge of the gill. Therefore the statements by Kellogg 

 (9, pp. 416-423, see also 7, p. 36), andPelseneer (12, p. 230) that the lateral 

 cilia in Lamellibranch gill-filaments serve mainly for straining the food- 

 particles or for interlocking the filaments require correction. There 

 can be no doubt, however, that the lateral cilia, as in Crepidula, may 

 help occasionally if necessary in washing particles towards the food- 

 groove by local reversed lashing. The long cilia found at the sides of 

 the frontal rows of cilia in many Lamellibranchs (see Eidewood's 

 figures iiassim as latero-frontal cilia, 13) are probably true straining 

 cilia. In Nucula, Anomia, Mytilus, Tapes, and Cardium, these are un- 

 doubtedly straining cilia. They stand out from the sides of the filament, 

 forming a sort of grating between them, and lash relatively slowly across 

 the length of and towards the middle of the frontal face of the filament 

 (see Figs. 15, 17, and 18). Thus Nucula and Mytilus have four kinds 

 of cilia, the lateral cilia producing the main current, the frontal for 



* That is, the side away from the exposed face of the gill-lamella. 



