CILIARY MECHANISMS OF LAMELLIBRANCHS 657 
Palps. In figure 22 the posterior palp (pp) has been pulled 
out from its natural position under the inner demibranch, and 
the anterior palp is folded forward. Figure 23 is a ventral view 
of the mouth region, with anterior palps (ap) folded forward, 
and shows the relation between palps and the inner demibranch 
(ig). It shows, perhaps better than other figures, the position of 
the narrow stream running in the proximal oral groove (pg) to 
the mouth (m), and the outgoing tracts on both palps above it. 
In all lamellibranchs the ciliation of the region about the mouth is 
similar to this. 
Material moving forward on the free ventral margin of the 
inner demibranch may be taken off on to any of the palp folds, 
to be. passed over them to the mouth (fig. 24). Too heavy a 
load will cause the folds to part and expose ventrally directed 
streams in ‘the grooves, which function as in Schizotherus. But 
if material is not removed from the inner demibranch margin 
to the palp folds, it continues forward, and is carried well into 
the proximal oral groove (fig. 23 pg); such a direct communi- 
cation between gill and oral groove is shown in several of the 
figures. It is evident that if more than a minute amount of 
material passes along this very narrow groove, it will be caught 
up by outgoing currents lying very close to it, near the mouth. 
This makes it extremely difficult to arrange an experiment so 
that material may be seen actually to enter the mouth opening. 
The ciliation of the dorsal margins of the palps is very unusual 
in that material is carried over them to the outer faces of the 
organs, and thence to their tips, the entire outer surface, in each 
case, directing currents posteriorly. 
Visceral mass. Figure 25 shows cilia currents below the line 
of gill attachment, over the liver mass (in stipple) and sexual 
mass to the ventral wall immediately behind the foot (f). 
Mantle. Collections are here moved to the fused and thickened 
edges, where they are led posteriorly, in the usual manner, to the 
base of the incurrent siphon (fig. 22). A view of this mantle 
edge is given in figure 26, in which the very small supplementary 
opening (so) is shown. The significance of this opening and a 
similar one in Lyonsia saxicola was not determined. 
