FOOT (A. W.) — ON ENTOZOA. 203 



and Poland. The few instances in which this worm has been found in 

 America were all cases of importation by travellers.* 



The geographical distribution of the Bothriocephalus of man being 

 certainly limited, we are in search of evidence to show if such is also 

 the case with the Bothriocephalus of the lower animals. There are 

 some facts which seem to admit of such a supposition. The Bothrioce- 

 phalus latus itself, according to Pallas, quoted by Leuckart, is not rare 

 in the dogs of Southern Russia, and Von Siebold has received it also 

 from a dog in Pomerania. Linnoous observed it also in Swedish dogs. 

 The Bothriocephalus cordatus has been found in considerable numbers in 

 the dogs of North Greenland, as well as in the human population. Of 

 twenty specimens recently described by Leuckart, nineteen were from 

 dogs, and one from the human body.f The portion of Tapeworm passed 

 by the Polar Bear — an inhabitant of those parts of Europe where men 

 are subject to the broad Tapeworm — is undoubtedly a part of one of the 

 Bothriocephalidae ; but whether it is the Bothriocephalus latus of man, 

 or to which of the twenty-five species of the genus it belongs, is diffi- 

 cult to decide in the absence of the head or the anterior part of the 

 6trobila. 



The development of the Bothriocephalidae is not so completely made 

 out as is that of the Tasniadae. In accordance with the general plan of 

 generation in the cestoid worms, the ova contained in the ovary of a 

 mature segment, or proglottis, of the broad Tapeworm, must find their 

 way into the body of some other animal, in which they will be deve- 

 loped to a certain degree, and no further, until that animal has been 

 devoured by some other, belonging to a higher species, to whose intes- 

 tine when they have been transferred, these hitherto only partially 

 developed worms will there attain their perfect and final condition. 

 What the animal is which receives and partly developes the eggs of the 

 broad Tapeworm, and which when eaten by man will be the means of 

 introducing into his body the Bothriocephalus latus, is the link which is 

 wanting. "We know that link in the case of the common Tapeworm — it 

 is the pig. "We can only conjecture it in the case of the broad Tapeworm. 

 There are reasons for believing that it is from fish the inhabitants of 

 those parts of the Continent of Europe where the parasite is endemic are 

 infected. It appears that the ova of the Bothriocephalidae are not ca- 

 pable of developing an embryo after their escape from the ovary of the 

 mature segment until they have been immersed in water for a period of 

 from four to eight weeks. \ After the expiration of this variable period, 

 the lid with which the egg is furnished opens, and permits the escape 

 of a fully developed ciliated embryo, which, after the rotatory fashion 

 of Volvox, swims about for several days, when the ciliated envelope 

 bursts, allowing the exit of a six-hooked non-ciliated embryo. These 



* Weinland, " Essay on the Tapeworms of Man," p. 59, quoted in Cobbold's " En- 

 tozoa," p. 292. 



f Cobbold, op. cit., p. 299. J Ibid., p. 293. 



