CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 



41 



(see the arrows marked C in Fio;. 10). They catch the food-particles which 

 tend to be drawn between the leaflets in the main current and pass them 

 on to the frontal cilia. The latter lash in a ventral direction, and thua 

 send particles along the edges of the leaflets to the ventral surface (see 

 Fig. 10, f .c. and the arrows marked B). Here a group of cilia now lash the 

 food-particles anteriorly towards the mouth to be eaten. As the food- 

 particles are lashed along the face of the gill they become embedded in 

 mucus, which is doubtless secreted by the epithelium of the gill. The 



DA. 



Ocd 



led. 



^^Syy TC. 



Fig. II. — Anterior view of a living pair of leaflets of the right gill of Nuciila. ( 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 effecting a junction with the mantle. 

 T.C. Cilia which transport collected food forwards. 



secretion of mucus on the Lamellibranch gill is indeed a matter of con- 

 siderable importance in the feeding process, and it is hoped to investigate 

 the matter more fully later. 



The examination of single living leaflets reveals a feature of much 

 interest in the ciliation of the gill. On the inner edges of the leaflets, 

 that is, on the ab-frontal surfaces, there occur numerous ciliated knobs 

 (see Fig. 10, c.d.). These ciliated knobs have cilia whose motion is like 

 that of the ciliated discs on the gill-filaments of the Filibranchia (for 

 example see the Fig. of Mussel, Orton, 5, p. 465). This motion may be 



