2 5 6 



The progressive stages of the disease were watched in 

 aquaria. Pathologically they are of great interest. In 

 the anal region a rounded projection makes its appearance, 

 augmenting rapidly in volume until it attains the size of a 

 small nut. It then presents all the external characters of 

 a cyst limited by a more or less transparent membrane 

 deprived of scales, and on whose surface blood-vessels 

 ramify. At the end of some days the cyst ruptures, and 

 the ligules escape by the opening. As to the fish, it does 

 not survive the accident. Such, according to what we have 

 ourselves seen and from the accounts of the fishermen, is 

 the ordinary mode of termination of the malady in our 

 country. Often enough, however, the tench die without 

 any rupture. In this case it is probable that the ligules 

 become free only when a portion of the flesh has become 

 destroyed by decomposition. They may, indeed, live a 

 long time amidst such surroundings. We preserved some 

 for several weeks in rotten fish, and they were still quite - 

 alive when we were obliged on account of the stench to 

 stop the experiment. It is a curious circumstance that, on 

 the other hand, those which we saw escape by the opening 

 of the cyst succumbed in a few hours on finding themselves 

 in the water taken from the Rhone, and frequently 

 renewed. One of them, of which a portion remained held 

 within the abdomen of the fish, presented the singular 

 phenomenon of one part of the body being dead whilst 

 the other was living. According to certain observers other 

 parts of the body, besides the abdominal and anal regions, 

 may equally afford means of exit for the ligules. Thus, 

 Block sometimes saw them escape by the belly, sometimes 

 at one of the sides, at the back or at the head, and some- 

 times even in the region of the tail. The wound left by 

 the worm is oblong like that of an open or bleeding vein. 



