NATURAL HISTORY OF THE BAY SCALLOP 
595 
FEEDING 
The principal organs for securing food, as previously noted, are the gills. For 
the scallop, as for some other forms, it seems clear that under certain conditions of 
feeding, as when much sediment is present in the water, they also enter into the proc- 
ess of selection (acceptance or rejection of filtered particles). For a description of 
the feeding currents and the location and functions of the various ciliated tracts see 
under “Gills.” Here it need only be noted that the gills bring in the food-laden water, 
separate food organisms and other particles from it, and convey these to the palps. 
The palps, as described by Kellogg (1910, 1915) and various workers, through the 
action of a complex and often puzzling arrangements of ciliary currents either pass 
the material to the lateral opening between the tufted lips or, if it be too coarse or in 
too large masses, through muscular action bring reverse currents against it and thus 
cast it away, near the foot, to be ejected near the byssal notch. 
Material not rejected passes into the transverse tube formed by the interlocking 
tufted lips, thence into the oesophagus, and thence, still by the action of cilia, into 
the stomach, where it again meets complex ciliation further complicated by the action 
of the style. 
No special study has been made of the food of the bay scallop. Apparently it 
does not differ greatly from that of other lamellibranchs in similar habitats and con- 
sists chiefly of the available plant and animal plankton of suitable size and shape, 
with nannoplankton playing an important part, and includes considerable quantities 
of the free moving microflora and microfauna of the bottom. In the relatively small 
number of stomachs examined by me, detritus sometimes bulked large, but whether 
it is important as food is not certain. Peterson and Jensen (1911) believed such 
material to be of greatest importance for the oyster. More recently Martin (1923), 
Hunt (1925), Savage (1925), and Yonge (1926a) have questioned the ability of lamel- 
libranchs to digest detritus such as that formed from Zostera and believed to consti- 
tute the larger portion of the organic content of coastal waters. Hunt (loc. cit.) found 
that the stomach contents of P. opercularis, from deep water, generally reflected the 
nature and variation of the plankton. Peridinians were especially abundant in the 
stomachs during late spring and summer, diatoms (important at all times) during 
fall and winter. 
CILIARY CURRENTS OF MANTLE, VISCERAL MASS, ETC. 
The ciliation of the mantle and other surfaces within the pallial cavity has been 
figured by Kellogg (1915) who studied both P. irradians and the sea scallop, P. 
grandis Solander ( P . tenuicostatus Mighels of Drew and Kellogg). In general my 
observations are in agreement with his. (Fig. 16a.) However, I found currents on 
the visceral mass of the bay scallop differing considerably from those shown by 
him for the sea scallop (compare 186 with 18c). These various ciliary currents 
convey material deposited upon them to points where it will be ejected with the feces 
or with material rejected by the palps. 
PIGMENTATION OF THE VISCERAL MASS 
If normally active scallops are opened and examined, the pendant visceral mass, 
tufted lips, and the outer surface of the palps '"are found to be more or less highly 
pigmented (as indicated in part by Fig. 3). This pigmentation varies greatly in 
intensity, but is always marked on the visceral mass except in “poor” or weak indi- 
