ENCYSTED CESTOIDEA. 33 



certain species of salmon, for instance; but in these it is met 

 with encysted in the liver and peritoneum, and is invariably 

 sexless. The examination of the livers of a great number of 

 the Salmo salvelinus caught in the Konigs-see, near Berchtesgaden, 

 recently convinced me that this worm can only attain to sexual 

 maturity in the alimentary canal of perch and pike. These livers 

 were covered with various sized cysts containing larger or smaller 

 individuals of Tricenophorus nodulosus, which were every one 

 sexless. The Cestoidea were obviously awaiting their sexual de- 

 velopment, which could only take place when they should have 

 passed into the intestine of a pike or perch, a migration which 

 may easily occur, since the lake is full of such predacious fish, 

 who are always ready to seize upon the salmon. When the 

 Tricenophorus nodulosus has come to sexual maturity and has 

 deposited its eggs in the intestine of the pike and perch, these 

 eggs will be passively extruded, since the cestoid embryos are 

 never hatched in the spot where they have been laid ; that is to 

 say, they will be expelled with the faeces through the anus of the 

 fish. With regard to the ultimate fate of the young of the 

 Tricenophorus nodulosus, I can state nothing from actual know- 

 ledge, but from what has been observed in regard to other intes- 

 tinal parasites, I think one may infer that the young of the 

 former will be impelled by the same instinct, to wander, and to 

 seek that situation which can alone develop their powers of repro- 

 duction. Although I am unacquainted with the form in which 

 the embryos of the Tricenophorus nodulosus commence their 

 wanderings, yet, having found tolerably large individuals of this 

 species encysted in the livers of various fishes (of salmon, 

 sticklebacks, millers' thumbs, burbot, blennies, and others), I 

 conclude that the young Tricenophori have merely made these a 

 temporary resting-place, and are waiting till their host becomes 

 the prey of the above-named fishes. Whether the young of the 

 Tricenophorus always avail themselves of an intermediate host by 

 whom they may be conveyed into the intestine of their final en- 

 tertainer, the pike or perch I cannot say. It is possible that 

 they may pass, at once, into the pike or perch whenever an 

 opportunity offers ; but under these circumstances it would be by 

 no means immaterial into which organ of the fish they first 

 entered. Since the intestinal canal is the only proper place for 

 their sexual development, they will, by passing into the liver or 



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