302 PARASITES OF ANIMALS 



cause of the terrible echinococcus disease, so prevalent in Iceland 

 and elsewhere. Experimental research, initiated by von Siebold, 

 has explained its origin ; Van Beneden, Zenker, and others have 

 also experimented successfully. Rarely attaining a length of 

 J" , the perfect strobile is made up of only three proglottides in 

 addition to the head, the lowermost segment being sexually 

 mature. As hydatids (Echinococcus veterinorum or E. hominis) 

 are found in a great variety of animals as well as in man, and 

 as these bearers form so many kinds of intermediate hosts, it is 

 easy to understand how readily dogs and wolves may acquire 

 the sexually-mature tapeworm. I am in possession of hydatids 

 from the liver of a clouded tiger (Fells macroscelis). In 

 England the Tcenia echinococcus is excessively rare, and has not 

 been seen in any dog which had not previously been subjected 

 to a feeding experiment. Mr Nettleship succeeded in rearing 

 large numbers. In Iceland, Krabbe found dogs to be infested 

 to the extent of 28 per cent., a proportion fully explaining the 

 prevalence of hydatid disease in that country. The remaining 

 tapeworms of the dog belong to the genus Bothriocephalus ; of 

 these, the broad tapeworm (B. latus) is best known, because it 

 infests man. Diesing has described a variety found in the 

 Pomeranian dog as a separate species (Dibotlirium serratum). 

 The museum of the Royal Veterinary College contains a very 

 perfect specimen of B. latus from an English dog, but the 

 parasite is of rare occurrence in this country. It is generally 

 supposed that this tapeworm is derived from the consumption 

 of fish belonging to the salmon and trout family, but Dr Fock, 

 of Utrecht, thinks that the bleak (Leuciscus albumus) is the 

 usual intermediate host. I have already discussed this question 

 at some length. Experimental proof is still wanting. In 

 addition to B. latus the dog is liable to harbor B. cordatus, B. 

 f'uscuSj and also two varieties of the last-named species (7?. 

 dubius and B. reticulatus t Krabbe). Taking the pit-headed 

 tapeworms as a whole, their prevalence in Iceland is not con- 

 siderable, amounting to about 5 per cent. only. Lastly, it may 

 be mentioned that instances are recorded of the occurrence of 

 the hog-measle (Cysticercus celluloses] in the dog. Though 

 many have felt sceptical on this point, Grurlt's authority is not 

 to be lightly set aside, confirmed, as it has been, I believe, by 

 MM. Megnin and Leblanc. 



Passing to the round worms it may be said that Ascaris mar- 

 ginata is, at the best, a mere variety of A. mystax of the cat, 



