632 JAMES L. KELLOGG 
experimentally, may easily be traced on the gills, but the very 
few observers who have examined the palps, have been confused 
by the numerous currents found there, and we have but very 
meager accounts of what has been supposed to occur on their 
surfaces. In Schizotherus, as in other lamellibranchs, certain 
cilia on the gill filaments drive the water of the mantle chamber 
into the basket-like interiors of the demibranchs, thus drawing 
a current through the incurrent siphon tube, and forcing one out 
through the excurrent, which is reached by the epibranchial 
chamber at the base of each demibranch. Suspended particles 
in the water, striking the mucus-covered gill surfaces, adhere to 
them, and, if in relatively large quantity, cause an instant local 
outpouring of a large supply of mucus. Experimentally, relatively 
enormous quantities of this secretion may be obtained from them 
in a short period. Particles, entangled in mucus, are carried 
to the free margins of all faces of both inner and outer demi- 
branchs, then forward in shallow open grooves. The anterior 
palp (ap) in the figure, is folded forward. In its natural posi- 
tion, it lies posteriorly, and over the posterior palp, the edge of 
the inner demibranch lying between them so that material from 
its groove is easily transferred to their applied faces. The 
edge of the outer demibranch (0g), however, lies entirely above 
the palps, and particles in its grooves are carried upward, around 
the front of the inner demibranch, in the distal oral groove, and 
then into the lateral oral groove, made by the union of the palps, 
on the side of the visceral mass. In many species, the outer 
demibranch has this position, as figures of several forms in this 
account show. Material transferred from gill to palp (near ref- 
erence letters 7g), as well as that coming from the vascular fold, 
starts across the large folds of the palp toward the lateral oral 
groove (lg). Whether it will continue in this course depends on 
conditions that, experimentally, may be determined at will. 
Courses taken by particles are the same on both palps. For con- 
venience, the posterior is most fully shown in the drawings. 
Palps. These organs in Schizotherus are of great size, and 
are capable of considerable contraction and extension. On the 
apposed faces are large folds, separated by deep grooves, while 
