346 Miscellaneoufi. 



distinguished an anterior protuberance, which was already visible in 

 the embryo when free in the water. The examination of the mol- 

 lusca did not furnish conclusive results. Most of the individuals 

 contained Cercariae ; but these belonged to several species ; so that it 

 was impossible to make out which of them were derived from Bis- 

 tomum 7ioduJosnm. However, by far the most abundant form in 

 Paladina impura was a species furnished with an aculeus, and re- 

 sembling D. nodalosum in the form and dimensions of its sucking- 

 disks. This Cercaria is developed in sporocysts, completely destitute 

 of structure, but often presenting a protuberance resembling that 

 seen in the larvae which penetrated into the interior of the Annelids. 

 The sporocysts increase by transverse division ; they never contain 

 more than a few Cercarise, and sometimes only a single one. In the 

 Paladina these Cercaria; become encysted, losing their taUs and at 

 the same time their aculeus, which the author saw detach itself. 

 Specimens of Paludina impura are found containing only sporocysts 

 and free Cercariae, others which contain only encysted Cercariae, and 

 others, again, with all three forms. 



The author administered the cysts to four small perch. These 

 fishes were opened two hours afterwards ; and in two of them M. von 

 Linstow discovered a certain number of young Distoma which pi-oved 

 to be B. nodulomm. These experiments therefore seem to prove 

 that the ova of these Trematoda fall into the water, from which the 

 embryos pass into Mollusca, from which they reach the fishes without 

 penetrating into an intermediate host. 



A curious fact observed in this species is its presence under a diffe- 

 rent form in Acerina cernua. The author has found on the outer 

 surface of the intestine of this fish delicate cysts which, when rup- 

 tured, gave issue to young specimens of Z>. nodulosuni, presenting all 

 the characters of the species. Some of them already possessed the 

 vitellogene and the germinogene, the testes and the cirrus-sac. 

 He has also found the same cysts with the same contents, together 

 with free young D. nodulosa in the same state of development, in the 

 intestine of Perca jiuviatilis, which they had evidently reached with 

 an individual of Acerina cernua. The walls of the cysts are much 

 more delicate than those occurring in Paludina impura ; the cysts 

 are also much larger, measuring 0-4 millim. or more instead of 0-07 

 millim. ; moreover the animal contained in them is much further 

 advanced in development. 



The author explains in the following manner the presence of the 

 parasite under these exceptional circumstances. There must be two 

 modes of transport of the Cercariae into fishes. In the first ease the 

 fish eats a Paludina containing encysted Cercariae ; the Cercariae are 

 set free by the digestion of the cysts and attain their sexual state in 

 the intestine of the fish. In the second case the Acerina cernua 

 eats a mollusk containing free Cercaria3, or else these larvae pass 

 directly into the fish. They pierce the intestine by means of their 

 aculeus and encyst themselves on the outside of the wall of that organ. 

 During their course through the intestine they increase in size, because 

 they find suitable nourishment there. 



Leuckart has laid down the principle that only the encysted Distoma 



