FOOD AND FEEDING IN FRESH-WATER MUSSELS. 
441 
FRESH-WATER MUSSELS. 
Posner (1875) concluded that food material is carried to the labial palps and 
moved forward by their cilia to the mouth. He shows a figure of a longitudinal 
groove in the lower edge of the inner gill for carrying material forward to the palp. 
Ortmann’s (1911) mention of this groove is not the first, as so considered by Bush 
(1922). 
Simpson (1900) stated that the flapping of the palps swept the material into 
the mouth, which idea is quite erroneous. 
Wallengren (1905) considered that the masses of material were brought to the 
labial palps and that cilia there swept them along to the mouth. He further 
stated that the minute particles that fell between the ridges on the palps were 
carried downward by cilia in the grooves and reached the lower edge of the palp 
and were thrown off. Another conclusion at which he arrived was that the cilia on 
the posterior side of the ridges on the palps beat forward and move particles along 
from crest to crest of the ridges, but that those on the anterior side of the ridges 
beat backward, and that on occasion the crests of the ridges, which usually lean 
forward, may be slanted backward. This would bring into play the cilia on their 
anterior slopes and material might be carried posteriorly off the palps by this 
means. 
Wilson and Clark (1912) mention a few algal forms, the lorica of the rotifer 
Keratella sp., and an Ascaris, that were found among the stomach contents of 
certain fresh- water mussels. 
Clark and Wilson (1912) found in the alimentary tract of a number of mussels 
“a large mass of muddy matrix” in which were mingled various diatoms, algal 
forms (Trachelomonas) , active “Euglena-like organisms,” loricas of rotifers, and 
fungus spores. Baker (1916) suggests that this “muddy matrix” is probably the 
kind of material described by Petersen (1911) as “dust-fine detritus.” 
Siebert (1913), after studying Anodonta cellensis Shrot, concluded that the cilia 
in the bottoms of the furrows on the apposing faces of the palps strike upward 
instead of downward, his findings being the direct opposite to those of Wallengren. 
Allen (1914 and 1921) has made a very thorough investigation of the feeding 
process in fresh-water mussels. He states that the food particles are carried into 
the mantle chamber by water currents induced by cilia on the gills and are inter- 
cepted on the surface of the gills by cilia there. Mucus is secreted about the parti- 
cles by certain cells of the gills, so that they are aggregated into clots. The material 
falling upon the outer surface of the outer gill is carried upward by ciliary action to 
the dorsal edge of the gill and then forward to the palps in the groove formed by the 
juxtaposition of the gill and mantle. That striking the inner surface of the outer 
gill moves upward to the dorsal edge, where it passes to the outer face of the inner 
gill. The cilia of this gill beat downward, and all material reaching it by any 
means is carried downward to the ciliated groove on the ventral edge. In this 
groove it is swept forward to the palps. Allen (1914), on page 130, says: 
Thus particles whieh find their way between the palps [that is, are brought there by the cilia 
of the gills] are carried to the mouth. As will soon be seen, very little undesirable matter ever 
reaches the mouth or palps, but even here Wallengren (1905) has pointed out how selection and 
rejection may be made. 
