Another distome was also found by Bilharz in the intestines of a young Egyptian boy. The largest known distome inhabits the liver of the _Balenoptera rostrata_, the little whale of thirty feet in length, which is regularly met with on the coast of Norway. The intestines of the ordinary seal often contain a very curious distome, which was first observed by Rudolphie, the _D. acanthoides_. The seal is also infested by the _Distomum cornus_, which some have incorrectly preferred to place in the genus Amphistoma. Besides the distomes which inhabit the liver, there are found but few in the mammalia, except in the Cheiroptera: these insectivorous animals have their intestines literally full of these parasites. We 200 have noticed the species which regularly frequent our bats, and it only remains to discover the insects by means of which they are introduced; for it is probable that these insects are infested by cercariæ during the time that they inhabit the water. Larvæ and their parasites ought to be carefully studied in the localities where bats abound. There are few birds, especially among the grallæ and the palmipedes, which do not enclose in their intestines a certain number of distomes. The same may almost be said of reptiles and batrachians, but it is especially in fishes that their number is greatly increased. We may say that there is no fish which does not nourish some of these trematodes. Among a portion of these, the cycle of evolution and transmigration is perfectly known; we may instance the _Distomum nodulosum_. This worm inhabits the intestines of the perch. The scolex, as well as the cercaria, has its particular characters, and we have long since found the latter in a fresh-water mollusc, the _Paludina impura_. The cercaria is easily recognized by the presence of two particular folds at the base of the buccal bulb, and by the transparency and the form of the extremity of the urinary apparatus. In the adult distome, this same part of the urinary apparatus encloses large vesicles with very distinct partitions. We may also mention among the distomes a species from fish, which has a great affinity with the singular distome observed by Bilharz, of which we have spoken above. This distome inhabits the "castagnole," or _Brama raii_. Under the opercula of this fish, the skin is folded, and forms one or more pouches, in each of which lives a coupled distome, 201 that is to say, by the side of each large and fat individual, full of eggs, there is one which is slender. It is the _Distomum filicolle_, to which the name of _Monostomum_ was at first given. We should be correct in supposing that of these two hermaphrodite worms one acts rather as a female, the other as a male. It is doubtless in this sense that Steenstrup maintained his assertion, that there are in nature no hermaphrodites.