T. B. ROSSETER ON EXPERIMENTAL INFECTION OF DUCKS. 401 



" Hamann found a Cysticercoid in Gammarus pulex which he 

 looks upon as the larval stage of this worm, and he assumes that, 

 as the domestic duck is the only bird (i.e. so far as Hamann 

 knows) which visits the water in which the larval stage was 

 found, this tapeworm is also found in domesticated ducks. An 

 argument like this has value in science only in order to place us 

 on our guard for the parasite ; but it would be altogether going 

 too far to accept this worm as a parasite of domesticated ducks 

 until it is found in that host. Hamann made no infections 

 with his larval forms, and accordingly the demonstration that 

 this Cysticercus represents the larval stage of Dre. tenuirostris, 

 is still lacking. 



"Von Linstow, 1892, observed the same larva in the same 

 host, and Marazek describes it from Cyclops agilis." — Stiles, loc. cit. 



These, then, are the three Cysticercoids with which I have 

 successfully infested ducks, and produced, as you have seen by the 

 mounted specimens which I have placed before you this evening 

 for your inspection microscopically, the perfect Taenia of each of 

 them; and thus have fulfilled, though unknown to Stiles, the 

 primary, and, in his opinion, the most important method of 

 rearing the adult stage. 



Respecting Cysticercus coronula. Both Marazek and myself 

 found this Cysticercoid in 1890 — I really discovered it in 1888, 

 but was ignorant at the time of its true character — parasitic in 

 Cyjyris ovum and Gypris cinerea ; and, although working inde- 

 pendently, and at so great a distance from each other (viz., 

 Preban, Bohemia, and Canterbury, England), we both diagnosed 

 it as the Cysticercus of Tcenia coromda. I formed this opinion, 

 and my conclusions were verified, by finding, on the edge of a 

 pond, an aggregation of tapeworms, which proved to be T. 

 coronula Duj., amongst the faecal matter of a duck which fre- 

 quented the pond from which the nurse, Gyirris cinerea, was 

 taken. For particulars I must refer you to Journ. Micro, and 

 Nat. Science, 1890 and 1891. 



Cysticercus gracilis is one of the earliest Cysticercoids I became 

 acquainted with, as in 1888 I found it making Notodromus 

 monachus its nurse. Singularly, I took the Notodromidse from 

 the intestine of a stickleback (Gasteroserus acideatus) ; and in the 

 same year I found it being nursed by Gypris cinerea and C. 

 viriens. It is by no means rare in the duckponds of this 



