The Morphology and Life-History of the Digenetic Trematode, Microphallus Similis (Jägerskiöld, 1900) Baer, 1943

The life-history of Microphallus similis has been worked out by experimental infection of both intermediate and final hosts. 2. Encysted metacercariae from Carcinides maenas developed to sexual maturity in Larus argentatus and Sterna hirundo. Eggs of the parasite developed in these hosts were used to infect Littorina obtusata. Two generations of sporocysts were recovered. 3. Littorina saxatilis and Littorina littorea also harbor the asexual generations at Woods Hole, Massachusetts. 4. The cercariae are minute, stylet-bearing monostomes and small green crabs, C. maenas, exposed to these cercariae became heavily infected; enormous numbers of larvae entered the tissues and developed into metacercariae identical with those of natural infections. Small crabs, each exposed continuously to the cercariae from six to eight infected snails, died in ten to twenty days and on dissection each yielded thousands of larvae. 5. The stages in the life-cycle of the parasite agree with descriptions by European investigators of corresponding stages: the metacercariae with metacercariae from C. maenas, described but not named by M'Intosh (1865); the adults with M. similis from Swedish gulls, described and named by Jägerskiöld (1900); and the cercariae with Cercaria ubiquita Lebour, 1907. The identity of these parasites as stages in the life-cycle of a single species is predicated.