700 JAMES L. KELLOGG 
cerning them. Streams on outer palp surfaces usually pass over 
the dorsal margins to the inner or applied faces. Those on the 
inner faces vary greatly in different genera, as will be seen by a 
comparison of the various figures. 
In several forms, parts of the visceral mass collections are 
passed to the palps. In all cases, the greater part, if not all, is 
cast into the mantle chamber. 
Though there is greater variation in the direction taken by 
streams on the mantle tracts than on other organs, all belong to 
the outgoing system, except in a few cases in which small amounts 
are passed on to the anterior palps. 
There is no selection or separation of food organisms from 
other water-borne particles. 
Volume alone determines whether the collected foreign matter 
that reaches the palps, shall proceed to the mouth, or shall be 
sent from the body on outgoing tracts. The gills of Yoldia and 
Pecten also have the power—by two entirely different mechan- 
isms—of directing their collections on to outgoing tracts when 
the volume of these is sufficient. 
A lamellibranch is able to feed only when waters are compara- 
tively clear—when diatoms are brought to the gill surfaces a 
few at a time. In muddy waters, all suspended particles, of 
whatever nature, are led to outgoing tracts. An exception is 
found in the sand-eating genus Macoma. 
All ciliated surfaces produce mucus, which appears locally 
in response to the stimulus afforded by the touch of foreign 
particles. Its amount is always that necessary to entangle the 
stimulating particles. Long continued stimulation of any 
surface may cause relatively enormous quantities of the secretion 
to be discharged. 
In several genera, the mantle develops, on each side, folds 
lying parallel with the edges, posteriorly (Schizotherus and 
others). These may enclose a waste canal where waste matter 
accumulates, until carried out of the incurrent siphon or siphonal 
opening, by a sudden reversal of its stream. A waste canal is 
made necessary by the presence of a siphon membrane which 
under certain conditions throws the entering water stream on to 
