Natural history and propagation of fresh-water mussels . fig. 8). The two parts or valves of theshell can be drawn together by a single adductor muscle,but, when the muscle is relaxed, they gape widely apartas shown in the illustration. There are also on theinner surface of each side of the body several pairs ofsensory cells with hairlike projections. It has beenassumed that the cells were sensory in function, andrecently L. B. Arey, working at the Fairport station,determined after detailed experiments upon severalspecies of Lampsilis and Proptera that there is a well-developed sense of touch
Natural history and propagation of fresh-water mussels . fig. 8). The two parts or valves of theshell can be drawn together by a single adductor muscle,but, when the muscle is relaxed, they gape widely apartas shown in the illustration. There are also on theinner surface of each side of the body several pairs ofsensory cells with hairlike projections. It has beenassumed that the cells were sensory in function, andrecently L. B. Arey, working at the Fairport station,determined after detailed experiments upon severalspecies of Lampsilis and Proptera that there is a well-developed sense of touch centralized in the hair cells. He regards the tactile responseas entirely adequate to insure attachment of the glochidium. In at least three genera of American mussels (several species of Unio, Anodonta,and Quadrula) the glochidium possesses a peculiar larval thread of uncertain signifi-cance (text lig. 8). This thread, so generally mentioned in textbooks based upon studiesof European mussels, is not found on the great majority of American species. We. Fig. 8.—Glochidium of Quadrula heros withgaping valves, seen from a side larval thread (/. t.) is seen betweenthe valves. Imier and outer sensory haircells (s. h. c.) are visible on each valve. 144 BULLETIN OF THE BUREAU OF FISHERIES. have observed it on glochidia of the following species: The washboard, Quadrula heros,the blue-point, Q. plicata, the pig-toe, Q. undata, the bullhead, Pleurobcvia cesopus, thespike. Unto gibbosus, the slop-bucket, Anodonta corpulcnta, and the river pearl mussel,Margaritana margariiifera. The squaw-foot, Strophitus edentulus, has a modified larvalthread (Lefevre and Curtis, 1912, p. 173). That the structure of the glochidium is less simple than appears to the ordinaryobserver is shown by the fact that, in the fully developed glochidium, close microscopicstudy will reveal the rudiments of foot, mouth, intestine, heart, and other organs whichwill not, however, assume their destined form and
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