468 



J. H. OETON. 



cilia on the tips of the inner leaflets lash the collected food anteriorly 

 towards the mouth. The latero-froutal cilia are also well developed 

 and, as in Mytilus, stand out between the filaments, acting as strainers 

 and lashing across the length of the filament away from the inter-fila- 

 mentary spaces. These cilia are very large, and, as in the case of all the 

 cilia on gill-filaments, it is necessary to see them living to obtain an 

 accurate idea of their size and function. And indeed all figiires of gill- 

 cilia ought to lie corrected, where necessary hy comparison loith the 

 living object. The ab-frontal cilia lash mainly towards the tip of each 

 leaflet as indicated in Fig. 18, and besides helping in producing the 

 main food and respiratory current, doubtless also assist in food- 

 collecting, by lashing food-particles around the tips of either leaflet- 

 On the outer dorsal edge of each leaflet of the gill of Nucula is a group 

 of large cilia (see Fig. 18). Those on the inner leaflets interlock with 

 similar cilia on the leaflets of the opposite side, while those on the outer 

 leaflets doubtless interlock with similar cilia on the mantle. Probably 

 these large cilia help in transferring food-particles from the dorsal to 

 the ventral surface, but their chief function is doubtless that of effecting 

 a junction between the right and left gills and between the gills and 

 mantle respectively. Between the ab-frontal and lateral rows of cilia 

 occur patches of cilia (see Fig. 18, c.d.) which are more numerous on 



.al}j:c. 



Oc.d 



led 



^^^,^^ 



Fig. 18. — Anterior view of a living pair of leaflets of tlie right gill of Nuenla. (x about 

 65.) The leaflets anterior to the pair depicted were cut away, 

 ab.f.c. Ab-frontal cilia. 



c.d. Patches of cilia on the inner and outer leaflets. 



D.A. Dorsal surface of gill about the 30th pair of leaflets from the posterior end of gilL 

 f.c. Frontal cilia. 



I. c.d. Cilia effecting a junction with similar cilia on the left gill. 

 I.L. Inner leaflet of gill. 

 I.e. Lateral cilia, 

 l.f.c. Latero-frontal cilia. 

 O.L. Outer leaflet of gill. 



O.c.d. Cilia eff'ecting a junction with the mantle. 

 T.C. Cilia which transport collected food forwards. 



