56 DR. H. LYSTER JAMESON AND DR. W. NICOLL ON 



conclusive fashion the correctness of his views in regard to the 

 hfe-history of the pearl-forming Trematode in Mytihos, and 

 towards that end an endeavour was made in 1901 to perform 

 feeding-experiments with a Pochard (^Fuligiola ferina), the only 

 likely diving duck which was available at the time. These 

 experiments were unsuccessful. 



It was in continuance of this work that the jDresent investigation 

 was undertaken. Ai^rangements were made* to obtain some live 

 Scoters {(Eclemia nigra) and have them fed upon mussels infected 

 with the pearl-inducing cercariae. Three Scoters were pur- 

 chased on our behalf by the Zoological Society from D. G. Schuijl, 

 of Rotterdam, who stated that they were all caught on the 

 Zwarte Water, in the province of Overijsel. In addition, four 

 dead Scoters, stated to come from the same locality, were kindly 

 sent to us for examination by the Superintendent of the Brighton 

 Aquarium. With one exception, these four birds were found 

 to be heavily infected with intestinal parasites, including a 

 considerable number of Gymnophalli. These will bo referred 

 to later. Of the three live Scoters, which were housed in the 

 Society's Gardens, one died shortly after ariival, and was found 

 to harbour numerous specimens of Tocotrema concavtim and 

 immature Cestodes in its intestine. The second Scoter was 

 removed to the Lister Institute with the object of making a 

 feeding-experiment, but it died within 24 houi's. Its intestine 

 contained only a few immature Cestodes. The third was kept from 

 8th to 24th December, 1911, when the experiment was started. 

 It was fed at intervals with mussels from the beds at Foulney, 

 near Piel, which were infected with the pearl-inducing Gymno- 

 phallus. Altogetlier about 1000 mussels were given to it. Check- 

 examinations of samples of these mussels showed that out of 

 78 mussels 32 were infected, the number of live Gymnophalli 

 being 64. On February 27th, 1912, the bird was killed and 

 thoroughly examined. The only parasitic worms present were a 

 few immature tapeworms in the intestine and two specimens of 

 Metoj^chis xanthosomus in the gall-bladder. 



It is difficult to draw any satisfactory conclusion from the 

 result of this experiment. At first sight the most obvious in- 

 ference would appear to be that the larva in Mytihts does not 

 become adult in (Edemia, but in some other host. This inference, 

 liowever, is not without objection, for, quite apart from the 

 evidence furnished by the close resemblance between the parasite 

 in the mussel and in the duck, other factors may require to be taken 

 into consideration — for instance, the somewhat unnatural mode 

 of feeding, the unsuitability of the season, the effect of cap- 

 tivit}", and so forth. In this connection, the complete absence 

 of other Trematodes from the intestine is significant, as suggest- 

 ing that the intestine may possibly have been cleared of parasites 

 as a result of digestive derangements following on change of 



* FTIianks to a grant from the Govcrament Grant Committee of the Eoysil 

 Soeiety.— H. L. J.] 



