470 PARASITES OF ANIMALS 



cissima obtained from the abdomen of the tench (Tinea vulgaris). 

 The interest of these experiments does not cease here, since they 

 afford a probable clue to the source of human BotkriocepKali, 

 which in nearly all essential points of structure correspond with 

 the Ligules. As remarked in the first part of this work, 

 Leuckart long ago pointed to the Salmonidae as probably 

 furnishing the intermediate host of this worm ; and he dis- 

 proved the views of Knoch, of Petersburg, who thought he had 

 reared Bofhriocephalus latus in the dog in a direct manner. I 

 have already called attention to the opinion of Dr Fock, of 

 Utrecht, who thinks the human bearer may become infested by 

 the consumption of the little fresh-water bleak (Leuci.^ <.-< 

 alburnus). From the observations of Dr Bertolus, it is 

 extremely probable that our Bothriocephalus latus is the 

 sexually- mature condition of Ligula nodosa infesting the abdo- 

 minal cavity and pyloric appendages of the common trout 

 (Salmo trutta). 



Another cestode of general interest is the Tricuspidaria 

 (Trianophorus) nodulosus, infesting many of our fresh- water 

 fishes. It varies in length from one to two feet. The seg- 

 mentation of the strobila is very indistinct, but the reproductive 

 organs occur at regular intervals. All parts of the body are 

 extremely contractile, especially the head. The tricuspid hooks 

 support thin chitinous laminae, which connect the two lateral 

 horns of each hook to the central apophysis. The object of 

 this arrangement is to afford additional security to the prong- 

 like processes. Van Beneden appears to think it an error that 

 the cusps of the hooks should have been figured in ' Kegne 

 Animal ' as directed forwards, and he has drawn the hooks 

 with the points downwards. In regard to the calcareous cor- 

 puscles, narrow vessels may be easily recognised passing off 

 continuously from the capsules in closing the particles. These 

 vascular prolongations are single, having their course directed 

 towards the epidermis ; doubtless they open at the surface, but 

 I did not detect any aperture. I have figured the tubes in 

 my f Entozoa ' (p. 132). Dr Guido Wagener figures similar 

 structures as occurring in Cercaria macrocerca. 



Various species of Tetrarhynchus dwell in the bodies of 

 sharks and rays, whilst their larvae inhabit fishes on which the 

 plagiostomi feed. Immature tetrarhynchs occur in cuttle-fishes, 

 but they are most abundant in such fish as the cod, haddock, 

 turbot, whiting (Fig. 81), flounder, sole, gurnard, mackerel, 



