18 ANIMAL PARASITES. 



tia') went over the statements .of the ancients, and gave a 

 natural history of these creatures as different species of the Tccnia 

 hydatigena (17GG, ' Misc. Zool./ p. 157) ; in 17G9 (' Stralsund. 

 Magaz./ i, p. G4), he described the Cysticercus tenuicollis from 

 the abdomen of Ruminants, and remarks that the watery vesicles 

 in question all agree in structure with the common tape- worms, 

 especially in the head, circlet of hooks, and sucking pits. They 

 are only less developed in the joints following the head, and they 

 also bear a larger or smaller vesicle of water at the caudal 

 extremity. According to him all cystic worms are forms of 

 tape-worms, and belong to a single species, " Taenia hydatigena = 

 Cystic tape-worm/-' which only presents some differences, espe- 

 cially in the caudal vesicle, according to the animal it inhabits. 

 He was also aware of the agreement of the head of the Cysticercus 

 of the mouse with that of the Taenia crassicollis of the cat (his 

 Taenia cucumerina, tab. ii, fig. 2). But neither Pallas nor Tyson, 

 by the denominations Taenia hydatigena, or Lumbricus hydropicus, 

 introduced by them for the cystic worms, wished to express 

 any opinion as to the genesis of these worms, or their derivation 

 from the ordinary tape-worms, however much we may be inclined 

 to suppose so. The originator of the unlucky theory of the 

 dropsical degeneration of the vesicular worms — a theory which 

 Pallas does not once mention — must have been Hartmann, who 

 appears to have referred to a dropsical degeneration from other 

 intestinal worms (Lumbrici) when he says, " An natura loci, non 

 sinens lougos formari lumbricos, corpus reliquum ob abundantiam 

 alimenti non concoquendam in utriculos extendit ?" 



As regards Pallas, he considers the Ccenurus of the sheep, 

 which was well known to him as a many- headed tape- worm, and 

 the Echinococcus, as nearly related to, if not identical with it ; and 

 at the same time thinks that the heads of Ccenurus in the former 

 case are only a further development of the globules observed in the 

 Echinococcus. Pallas also (' Neu. Nord. Beitr.,' i, p. 58) states 

 that he introduced the small red eggs of the Taenia cucumerina of 

 the dog through a small wound into the abdominal cavity of a 

 young dog, and after the lapse of a month found there small tape- 

 worms less than an inch long, and with very short segments. 

 This is very improbable, and, I think,a complete mistake. 



Besides Pallas, Statins Miiller and Otto Fabricus, to whom 

 the discovery of the animal nature of the Cysticercus of the pig 

 is sometimes erroneously ascribed, introduced more svstem into 



