FISH PARASITES. 121 



various small fresh-water fish, upon the blood of which it 

 subsists, sometimes to the destruction of its victim. It is 

 the Monoculus foliaceus of Linnaeus, 

 and its natural history and structure, 

 in the different stages of its exist- 

 ence, have been detailed by the 

 younger Jurine in the most satisfac- 

 tory manner, in the seventh volume 

 of the Annales du Museum d'His- 

 Arguius foiiaceus. u toire Naturelle. The first pair of legs 

 is large and short, and shaped some- 

 what like a cup, since it is by these 

 organs, which probably act like a 



cupping machine, that the insect attaches itself to small fish. 

 The young resemble their parents in form, though their lo- 

 comotive organs are very differently constructed. The other 

 genus, Caligus, is destitute of the large cup-shaped feet, the 

 anterior pair being hooked. The tail is long, and terminated 

 by two very elongated processes in the females, of which 

 the use has not yet been determined. These animals are 

 termed fish-lice, being parasitic upon various kinds of fishes. 

 The genus has been subdivided into several sub-genera by 

 Leach and Latreille. 



The Dichelestionidee is composed of the single genus Di- 

 chelestium (Hermann), having the body long and narrow, com- 

 posed of seven segments, the first of which is larger than the 

 rest, with a pair of slender filiform antennae, a pair of short 

 didactyle claws, a tubular sucker, three kinds of feelers, four 

 short legs for prehension. These animals insinuate them- 

 selves into the flesh and the gills of the sturgeon, as many 

 as a dozen having been found upon one fish, retaining firm 

 hold of their prey by means of their strong frontal pincers. 



