CILIARY MECHANISMS OF LAMELLIBRANCHS 695 
water, they leave the body through the excurrent siphon. In no 
other gills that I know of except those of Monia, and Pecten, 
are there special means of conducting undesirable material to 
outgoing tracts. In other cases, collections may be of such 
volume that the marginal groove cannot hold them, and they 
fall into the mantle chamber of their own weight. It is the 
function of other gills simply to collect, and pass collections on 
to the palps on which it is determined whether they shall be con- 
tinued on to the mouth, or to an outgoing tract; but here the gill 
possesses its own outgoing tract, which must inevitably be used 
unless contact is effected between gill and palp. 
Palps. The huge lateral extensions of these organs are for 
some distance suspended from the overhanging digestive gland 
(fig. 67, vms). Behind the line of this attachment, and as far 
toward their free ends as the origin of the appendage, their dorsal 
margins continue to be united, and on the outside along the line 
of this union is the groove (fig. 70, lg) the function of which ap- 
parently is to receive the gill coliections. This groove, so far as 
I know, has never previously been seen. From its position in 
reference to the ventral surface of the gill, from the direction of 
its cilia-currents, and from the fact that its margins may convert 
it into a nearly closed tube, or open so fully as to expose it, I am 
convinced that it has been constructed to receive gill collections, 
though I have no record of having seen the transfer actually 
made. 
Gill collections and the palps. Drew, from his study of the 
gills and palps, concluded that the former were not food col- 
lectors, as Mitsukuri (’81) had done, also. He says: 
Experiments were tried to determine, if possible, the part taken 
by the gills in the collection of food. . . . No definite results were 
reached, but they were not observed actively engaged in collecting 
food. Considering the remarkable activity of the palps as collectors of 
food, such activity for the gills seems rather unnecessary, and it would 
also seem that the pumping action of the gills would seriously interfere 
with their normally performing such a function. 
Drew had not seen the extension of what I have called the 
lateral oral groove, but I am puzzled to know how the tremendous 
