CILIARY MECHANISMS OF LAMELLIBRANCHS 697 
assumed, and not actually observed, that these extensive ap- 
pendage collections passed to, and entered, the mouth. Yet it 
may be said that if they do not, but are usually cast away, itis 
hard to understand why they are made at all. Nevertheless, 
in very many observations, extensive collections by the append- 
ages were invariably conducted out of the body on outgoing tracts. 
It has been shown that large accumulations, brought to the 
gateway x by appendage or oral groove, are taken up by the 
dorsal margin tracts and cast into the mantle chamber from the 
palp tips. There is still another and very remarkable outgoing 
tract that. may be brought into operation at this point and 
throughout the groove (lg) shown in figure 70. The anterior 
wall of this groove is thick, rounded, and capable of no movement. 
Collections are brought over it from the outer surface of the 
anterior or outer palp. The posterior lip of the groove, continu- 
ing out on the dorsal margin, is very thin and flexible, and on its 
outer face (to the left of reference letters, Ig) is a strong cilia 
current directed upward. Its course is easily followed, and its 
loads are seen to be transferred to the inner face of the suspending 
membrane of the gill (above reference letters gm in figs. 68 and 70) 
Here this waste matter from the palp passes into the epibranchial 
chamber of the gills, and leaves the body through the excurrent 
siphon. This flexible groove margin receives its material chiefly 
from the groove, by rolling over into it in response to the stimulus 
of a large amount of material, a process similar to the cleaning 
action of the ventral margins of such palps as those of Schizo- 
_therus or Mytilus, where, by an upward folding, or a spiral twist- 
ing of the entire organ, they are brought in contact with the 
folds. 
Palp folds. The palp folds are numerous, and are continued 
forward very much nearer to the mouth than is usual (as 
shown in the view of the mouth region represented in fig. 72) 
so that the proximal oral groove (pg) is very short. It is note- 
worthy that the palp folds nearest the mouth are the smallest, 
and that they become very large near the palp tip (fig. 70), the 
reverse usually being the case. The chief current is directly 
across the folds toward the mouth, while in the grooves, and 
