CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 



39 



€nds touch the mantle postero-ventrally (see Fig. 7), and the lower 

 portions of the gill on each side also meet ventrally, while the tips of the 

 upper lamellae complete the partition of the mantle cavity by forming a 

 junction with the mantle dorsally. Thus a large anterior inhalent chamber 

 and a smaller posterior exhalent one are formed (as shown in Fig. 9), in the 

 same way as in Anomia aculeata and the higher Lamellibranchs. This 

 subdivision of the mantle cavity is of some importance, as it has been 

 regarded by some authors (for example, Sedgwick, p. 345) as occurring 

 only in the higher Lamellibranchiata. It will thus be seen that the whole 

 of the gills of Solenomya resemble generally one lamella of the gill of a 

 mussel for example. 



Fig. 9. — View of a living specimen of Solenomya togata to show the relations of the gill 

 and the inhalent and exhalent chambers. ( x ca. 10.) 

 G. Left gill. 



I.C'h. Inhalent chamber. 

 E.Ch. Exhalent chamber. 

 A. Anterior end. 



P. Posterior end. 



D. Dorsal surface. 



U.l. Upper lamellae of gill. 

 L.l. Lower lamellae of gill. 



J. Anterior end of the fused portion of the mantle. 



T.C. Region where collected food is transported forwards as shown by the arrow. 



The gill of Solenomya, it w^ill be remembered, has the outer and inner 

 leaflets of the same side placed vertically, the one over the other, so that 

 both appear to form one leaflet with a shallow groove along the median 

 lateral line (see Fig. 9). These leaflets are arranged on an axis on each 

 side at the posterior end of body with only the thin edges of the leaflets 

 showing in a side view. The shape of a pair of leaflets may be seen in 

 Fig. 10. 



On feeding the animal with carmine grains it was observed that the 

 food-particles collected on the outer faces of the gills were transported 

 quickly to the ventral edges — even from the upper leaflets — and thence 

 carried forwards towards the mouth to be eaten. The collection and 



