TEANSMIGRATIONS AND METAMORPHOSES. 197 



ists to discover their abode and determine their identity. 

 Considering the number of observers who have mentioned 

 these distomes, it is evident that these parasites must 

 be very common. We find the names of Euysch, Leeu- 

 wenhoek, Swammerdam, Camper, Houttuyn, Mulder, 

 Heide, Biddloo, Snellen, etc., among the naturalists 

 who have made them a subject of study. In our own 

 day, the writers who have explored- this territory are so 

 numerous that we should require more than a page 

 simply to give their names. 



-Distomes frequent, with few exceptions, all the classes 

 of the animal kingdom, and if their number is great 

 among fishes, they are not less numerous in mammals 

 and birds. The higher classes of animals usually inocu- 

 late themselves through the intermediation of molluscs, 

 worms, and crustaceans, and it is therefore in the ranks of 

 these that we must seek for their first abode. Without 

 admitting that their size bears some proportion to the 

 host which gives them shelter, still, the largest species, 

 the Distomum Goliath, is found in the liver of one of the 

 balaenoptera. This distome is of the size of a large leech, 

 and its host does not measure less than twenty metres. 



Mons. Willemoes-Suhm mentions a distome which at 

 the time of its cercarian evolution lives freely in the 

 water, and attaches itself by its sucker to the larvae of 

 worms or copepod crustaceans, and then lodges in their 

 dejecta without encysting itself. This is the Distomum 

 ocreatum of the herring, according to Professor Moebius. 

 Mons; Ulialnin found in the bay of Naples another free 

 distome, which is also attached by its ventral sucker to 

 certain copepods, and which becomes the Distomum 

 ventricosum inhabiting many kinds of fish. 



