698 JAMES L. KELLOGG 
apparently always exposed, are narrow, dorsally directed tracts 
which tend to work material upward to the extremely narrow 
lateral oral groove (lg, fig. 72). No ventrally directed tracts 
were seen. 
Mouth region. Figure 72 represents a very interesting cili- 
ation. Here the anterior palps (ap) have been folded forward, 
and the posterior (pp) backward. Instead of forming continu- 
ous lips in front of and behind the mouth (m) as is usually the 
case, there is nearly a complete break on the median line, the 
ventral edge of the anterior fusing with the mantle, which here 
stretches across between mouth and anterior adductor, about 
midway between letters m and mo. The ventral margins of the 
posterior palps, on the other hand, independently enter the 
mouth vtself, and extend for some distance into its cavity. 
In most lamellibranchs, material may approach the mouth 
only along the very narrow line of the oral groove (lg and pg) 
for near the mouth this is bounded by outgoing tracts; but here 
it may enter all along the sides of the opening. But even after 
actually entering, it may still be caught up by outgoing tracts, 
and ultimately be discharged from the body, and this invariably 
happens in experiment, when more than a very small volume of 
material attempts to enter at a time. This is repeated again 
and again on tracts leading to the mouth in nearly all lamelli- 
branchs. If material is to enter the digestive tract, it must be 
conducted to it in narrow streams, and a little at a time. 
The outgoing streams from the mouth opening are three in 
number. Qne is on the median line anteriorly, and leads, right 
and left, to the mantle wall. Another, corresponding to it, is a 
broad tract from the posterior mouth edge, and leads out on to 
the visceral mass. The third is found on the ventral margins of 
the posterior palps, and extends into the mouth itself. Here, 
however, the outgoing streams appear not to be exposed directly 
to the mouth cavity, but are on those sides of the palp edges 
which are next to the wall. They can be exposed, and have 
been seen to bear out material that had fairly entered the mouth. 
Mantle. There is a general ciliation of mantle walls, with no 
distinct tracts, collections being carried ventralward and back- 
