FOOD AND FEEDING IN FRESH-WATER MUSSELS. 
445 
LAMELLIBRANCHS IN GENERAL. 
Erman (1833) stated that the food of lamellibranchs was carried forward in 
currents set up by the action of the cilia and then fanned into the mouth by the 
palps. 
Thiele (1886) considered that the structure and position of the palps showed 
that their chief function was to transfer to the mouth the food collected by the gills. 
MacAlpine (1888), however, from observations made upon detached portions 
of the palps and gills, concluded that they take no part in the feeding process but 
carry away foreign material. 
Lotsy (1893), working with marine clams and oysters, concluded that they 
can discriminate between various sorts of food material, but made no statement 
relative to the mechanism by which this was accomplished. 
List (1902) stated that in "die Mytiliden” all foreign bodies that reach the 
palps are carried into the mouth if they do not exceed a certain size. 
Petersen and Jensen (1911) showed that the organic debris resulting from the 
disintegration of eelgrass, etc., forms a very important item in the food of marine 
invertebrates. 
Blegvad (1914) reached the conclusion that "Detritus forms the principal 
food of nearly all the invertebrate animals of the sea bottom, next in order of impor- 
tance being plant food from fresh benthos plants.” 
Grave (1916), working with oysters, concluded that considerable choice of 
food material was exercised by means of a reversal in the direction of the beating 
of certain cilia of the palps. He refers to Parker’s (1905) experiments in which a 
reversal of the cilia was found in Metridium in response to certain stimuli such as 
crab juice and the like. In this paper Parker calls attention to the observations 
of Purkinje and Valentin (1835), in which they noted spontaneous reversal of the 
cilia on the "accessory gills” (Nebenkiemen of Purkinje and Valentin) of the 
mussel, and to the fact that these observations were confirmed by Engelmann 
(1868, 1879, and 1898). Grave disagreed emphatically with the conclusion of 
Kellogg that lamellibranchs do not feed when the water is too full of sediment, 
offering as proof the results of the examination of the stomach-contents of a num- 
ber of oysters kept some hours in very turbid water. These oysters had ingested 
great numbers of food organisms and also great quantities of sediment (italics are 
the authors’) . After a period of 14 days the oysters kept in this very ttu-bid water 
had made "perceptible growth of shell.” Grave thought that there was a reversal 
of the beat in certain cilia on the palps by which sufficient silt was removed from 
the palps to allow feeding to proceed. 
Mitchell (1918) found that oysters kept in solutions of dextrose absorbed this 
sugar and converted it into glycogen. 
Nelson (1920) described the ingestion of great quantities of carmine particles 
by veligers of oysters. These veligers have no palps, and Nelson stated that this 
is the reason that the carmine was not discriminated against and separated from 
the food material. In his 1921 paper he showed by conclusive experiments that 
oysters "continue to feed in waters bearing as high as 0.4 gram, dry weight, of 
