274! BERGHj ON THE EXISTENCE OF 



hours— a fact of which experience has assured us. M. Valen- 

 ciennes makes the same remark with respect to the Cysticerci 

 of the pig. It is consequently very difficult to admit a priori 

 that the Caenuri of the sheep can reach the intestine of the 

 dog in the living state. And besides this, the circumstance 

 that the head of the encephalic entozoon of the sheep dift'ers 

 enormously in size from that of the intestinal parasite of the 

 dog, renders it extremely doubtful that the one can possibly 

 proceed from the othqr. 



In the absence of further proofs we can scarcely believe 

 that a microscopic embryo of a Tcenia, hatched in the intes- 

 tine of a sheep, should be able to bore its way as far as the 

 brain of a ruminant, and there become transformed into a 

 vesicle capable of developing numerous scolices, to make use 

 of an expression of M. V. Beneden^s, whilst all the embryos 

 of the other Tanice are capable merely of being developed 

 temporarily as individuals in any situation where their inex- 

 plicable peregrination may be arrested. 



We have shown to several members of the Academy portions 

 of sheep^s intestine absolutely obstructed by the multitude of 

 Taenias. This has been repeatedly observed by one of us. 

 These ruminants, however, never feed upon pork, nor upon 

 rabbits, nor upon any flesh infested with Cysticerci. If these 

 tapeworms are so well contented with the intestine, why on 

 earth should some among them set off, amidst so many diffi- 

 culties, in search of the brain, in order there to undergo a 

 metamorphosis, to which the rest are not subjected? How 

 does it happen also that in dogs kept isolated we should meet 

 with more than double the number of Tsenias than we have 

 administered of Ccenurus-heads ? 



On the Existence of Urticating Filaments in the 

 MoLLUscA. (Om Forekomsten af Neldefiim, &c. 

 Vidensk. Meddel. fra den nat. Foren for Aaret, 1860. 

 Andet Parti II, p. 309. Copenhagen, 1861.) By Dr. 

 Bergh. 



The prehensile threads, noAV generally termed '' urticating 

 organs,^' were discovered in 1835, in the Hydra, by Corda 

 and by Ehrenberg. About the same time they were found 

 by R. Wagner in the Actiniae, who at first regarded them as 

 zoosperms. Subsequently, however, he recognised their 



