THE MORPHOLOGY AND LIFE-HISTORY OF THE DIGENETIC TREMATODE, MICROPHALLUS SIMILIS (JAGERSKIOLD, 1900) BAER, 1943 x HORACE W. STUNKARD U. S. Fish and Wildlife Service and the American Museum of Natural History, Nczv York 24, N. Y. Although significant observations had been reported earlier, the first complete life-histories of microphallid trematodes were worked out by Cable and Hunninen (1940) and Rankin (1940b). MTntosh (1865) had described and figured larval worms from the tissues of the green crab, Carcinides niaenas (Linnaeus), taken at St. Andrews, Scotland, but the life-cycles of trematodes were quite unknown at the time and MTntosh described the structures as eggs, each of which contained a tiny worm that he surmised became a sexually mature distome in "such fishes as the Cotti, Gadi, and others," which feed on the crustaceans. He reported a speci-men of Cottus bulbalis, about a foot long, with (p. 204) "two entire specimens of Carcinus maenas, each upwards of two inches across the carapace, in its stomach, besides the partially digested debris of others." His descriptions and figures identify the worms as members of the genus Microphallus and with considerable certainty as M. similis (Jagerskiold, 1900). Although measurements were not given, his Figure 5 of an excysted specimen shows the suckers to be of approxi-mately equal size and the "small globule" (seminal vesicle) anterior to the acetab-ulum, together with the size of the gonads, evidence full development of the meta-cercaria. Levinsen (1881) described adult trematodes from the eider duck, Somateria molissima, taken at Egedesminde, Greenland, as Distoma pygmaeum and Brandes (1889) described similar worms from Tringa alpinus as Distoma clavijorme. Jagerskiold (1900) described specimens from Swedish gulls, Larus argentatus and L. fuscus, as Distoma pygmaeum var. simile. Other species have since been described from different hosts in other parts of the world. Ward (1894) described worms from American lake-fish as Distoma opacum and noted their similarity to D. pygmaeum. The parasites occurred in Amia calva, Ictalurus punctatus and Perca flavescens, and encysted larval stages were found in the crayfish, Cambarus propinquus. With the dismemberment of the old genus Distoma, Stossich (1899) erected the genus Levinsenia to include Distoma brachysomum Creplin, 1837, D. macrophallos von Linstow, 1875, D. pygmaeum Levinsen, 1881, and D. opacum Ward, 1894. Liihe (1899), but not Looss (1899), as has been claimed (cf. Looss, 1902: p. 704) designated L. brachysoma, and Jagerskiold (1900) proposed L. pygmaeum, as type of the genus Levinsenia. Noting differences between D. brachysomum and D. opacum. Ward (1901) named the latter species type of a 1 The experimental work was done at the Marine Biological Laboratory, Woods Hole, Massachusetts, during the period May 1 to October 31, 1956. 254
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