530 Bulletin American Museum of Natural History [Vol. LIII 
Infusoria, Desmidiacez, and other lower alge. In the absence of these, 
they also attack higher aquatic plants and Lymnza is said to be particu- 
larly fond of duckweeds (Lemnacez).? The muscular gizzard of Lym- 
nza usually contains much sand and it appears from H. 8. Colton’s® 
observations that, unless such fine grit is present, the snail is unable to 
feed upon higher aquatic plants. There are among the fresh-water 
snails but very few normally carnivorous species, such as Vzvzparus, 
which, according to Geyer,‘ explores the mud with its snout in search of 
worms. Certain species, however, take to an animal diet under abnormal 
conditions. Lymnza, Planorbis, and Physa have heen repeatedly ob- 
served feeding upon meat or, in captivity, attacking other mollusks or 
their own eggs. | 
Interesting ccenobiotic relations exist between most mussels of the 
family Unionide and certain fishes. In this family the larva, known 
as glochidium,® is enclosed within two minute shells furnished with 
strong hooks by means of which it fastens itself to the body of a fish. 
These larvee are emitted in slimy masses by the mother mussel, when they 
sink to the bottom and remain resting on their dorsal side, with the 
valves gaping upward and a long filament (usually regarded as a byssus). 
streaming up into the water above them. If a fish comes within reach 
they close and open the valves violently and rapidly so as eventually to 
grasp the surface of their host. The glochidium then remains attached to 
the gills or fins of the fish for a number of weeks, enclosed in a sort of 
cyst, consisting of the epithelial cells of its host.’7 Certain species of fish 
i Hrochiney H. 1898. ‘Stisswasserschnecken als Planktonfischer.’ Forsch. Ber. Biol. Stat- 
6n,. Vb; Dp: f 
ees O. 1907. ‘Planktonalgen als Molluskennahrung.’ Arch. Hydrobiol. Planktonk., IT, 
pp. 358-361. 
Allen, W. R. 1914. ‘The food and feeding habits of freshwater mussels.’ Biolog. Bull., X XVII, 
pp. 127-146, Pls. 1-11. 
Churchill, E. P., and Lewis, Sara I. 1924. ‘Food and feeding in fresh-water mussels.’ Bull. U. 
S. Bur. Fish., XX XIX, (1923-24), pp. 489-471, 9 Pls. 
A eee. H. M. 1875. ‘Ueber den Darmkanal einiger einheimischen Gastropoden.’ (Stras- 
ourg). 
31908, Proc. Ac. Nat. Sci. Philadelphia, p. 424. 
4Geyer, D. 1909. ‘Die Weichthiere Deutschlands.’ (Stuttgart), viii+116 pp., 3 Pls. 
ae ae an account of such cases by Pelseneer, 1920, Mém. in-8° Ac. Belgique, Cl. des Sci., (2) V, pp. 
6The glochidia found in fresh-water mussels were at first believed to be independent parasitic organ- 
isms of these mollusks. C. G. Carus (1832, ‘Neue Untersuchungen tiber die Entwickelungsgeschichte 
unserer Flussmuschel.’ Nova Acta Ac. Nat. Cur. Dresden, XVI, 1, 87 pp., Pls. 1-1v (first showed that 
they were the embryos of Unionide. 
7This curious development of the early stages in the Unionide was first discovered in Anodonta by 
Forel, F. A. 1867. ‘Hinige Beobachtungen tiber die Entwicklung des zelligen Muskelgewebe. Bei- 
trige zur Entwicklungsgeschichte der Najaden.’ (Wiirzburg), 40 pp., 3 Pls. 
See also Faussek, V. 1903. ‘Parasitismus der Anodonta-Larven.’ Mém. Ac. Sci. St. Pétersbourg, 
&Cl. Sc. Phys. Math., (8) XIII, No. 6, pp. 1-141, Pls. 1-vii (in Russian). 
Le Févre, G., and Curtis, W. C., 1910. ‘Reproduction and parasitism in the Unionide.’ Journ. 
Exper. Zool., [X, pp. 79-115. 
Surber, T. 1913. ‘Notes on the natural hosts of fresh-water mussels.’ Bull. U. 8S. Bur. Fish., 
XXXII, (1912), pp. 101-116, Pls. xxrx-xxx1. 
Howard, A.D. 1914. ‘Experiments in propagation of fresh-water mussels of the Q uadrula group.’ 
U.S. Bur. Fish. Doc. No. 801, 52 pp., 6 Pls. This author credits Leydig with the first discovery of the 
parasitism of the larve of fresh-water mussels upon fish, evidently through confusion with the reverse 
parasitism of young fish upon Unionide (see below). \ 
