716 OCCURRENCE AND DEVELOPMENT OF BOTHRIOCEPHALUS LATUS. 



have found their way thither not long before, 1 led me to think that not 

 fishes, but perhaps smaller aquatic animals, such as Naiadse, which 

 harbour the related tape-worm Archigetes, might be the intermediate 

 hosts of Bothriocephalm. 



In opposition to Bertolus and myself, Knoch lays but little stress 

 in the process of infection on the ciliated embryos. He attributes to 

 them only the rdle of increasing the range of distribution, and 

 facilitating the transmission of the embryo. From his feeding 

 experiments, he concludes that this ciliated stage is not necessary in 

 the life-history of the parasite. Infection is effected equally well, and 

 indeed more frequently, by eggs, and it is indifferent whether these 

 contain an embryo or not. It occurs, as in the Tcenice, even when 

 proglottides with ova are conveyed to the alimentary canal of the 

 future host. There is no change of host, the transmission of the ova 

 is directly followed by the development of the sexually mature form, 

 so that man acquires the Bothriocephcdus, not from fishes or lower 

 animals, but directly from eggs or embryos which he has swallowed, 

 usually in drinking water. 



In support of these assertions, Knoch cites, as we have said, the 

 results of the experiments made by him on dogs and other mammals. 

 In seven different cases these were fed partly with ova, and the 

 associated proglottides, partly with the ciliated embryos. Investiga- 

 tion of the victim, sometimes after several weeks, sometimes only after 

 months had elapsed, gave in three cases (in a dog, 

 a cat, and a rabbit) entirely negative results. 

 In the other instances, which were all dogs, 

 Botkriocephali were found in the gut, but only 

 a few (at most seven, and in one experiment, 

 made by Pelican, only one), and these at very 

 different stages. Although the number of parasites 

 contrasted strikingly with the hundreds and 

 thousands of ova used for feeding, and although 

 the degree of development did not seem to agree 

 with the period which had elapsed, Knoch was 

 ture ova. After Knoch so convinced of the cogency of his experiments, 

 that he forthwith declared the result as requir- 

 ing no further confirmation. And this opinion persisted even till a 

 time when I had for long emphasised the insufficiency and the 

 inadmissibility both of the proof and of the method of experiment, 

 noting that the dog under ordinary circumstances can by no means 

 be regarded as free from Bothriocephali, as was asserted by Knoch, 

 but is, on the contrary, according to both older and more modern 



Sitzsb. Dorpater Gcs. f. Naturw., Feb. 1871. 



