CILIARY MECHANISMS OF LAMELLIBRANCHS 677 
versal posteriorly directed current along a plain ventral margin, 
seems not to be present. 
Visceral mass. Currents on the visceral mass of Pecten are 
represented in figure 45. In the region of the foot (f) collections 
from a considerable area are carried forward to the posterior 
palp (p). On the remainder of the wall of the body, collections 
are carried posteriorly and thrown off into the mantle chamber 
along the side extending from the pointed posterior end to the 
adductor muscle (a). The ciliation is practically the same in 
P. irradians, except that, posteriorly, material is all cast from the 
pointed tip. 
Mantle. It is shown in figure 46 (P. tenuicostatus) and 47 
(P. irradians) that the greater part of the mantle collection is 
carried to a position above the rectum (r). <A less amount, 
most of it gathered from the mantle edge, is carried to a cor- 
responding position on the ventral side. At these points, in 
P. tenuicostatus, the material is forced into well defined vortices 
(v,v) where relatively large collections are made. These are 
discharged from the body by a sudden, but not complete 
closure of the valves. There are no vortices on the mantle of 
P. irradians, but at corresponding positions, currents carry 
material over the mantle edge, often aided by a closing of the 
valves. Between the points x and y on the posterior face of the 
adductor muscle, some material is deflected on to the muscle 
wall, from that to the suspending membrane of the gill, from 
whence it falls once more to the mantle, the adaptation in the 
course taken not being apparent. 
Ostrea virginica 
Gills. On all gill lamellae, collections are carried to the mar- 
gins, and moved in grooves toward the palps. At the base of 
each lamella there is also a tract carrying material forward. 
Fig. 49 Ostrea lurida; mantle ciliation; ga, line of gill attachment; x, a line 
over which waste is expelled. 
Fig. 50 Pholadidea penita; aa, anterior adductor; b, bay of mantle; fo, foot 
opening through mantle; g, gill; p, anterior palp; s, siphon; vms, visceral mass. 
Figs. 51 and 52 Pholadidea penita; detail of palp ciliation; dm, dorsal mar- 
gin of palp; fd, palp folds; vm, ventral palp margin; «, course taken by a small 
amount of material; y, ciliation across the folds. 
