MANUAL OF NATURAL HISTORY. 309 



3. FAMILY. Lerneans -Proper (Lernseidse). Head 

 furnished with horns ; antennae none ; a 

 single pair of curved jaw-feet ; no brachi- 

 form appendages. 



IV. ORDER WOKM-LIKE FlSH-PAKASlTES 



(Helminthoidea). 



Body worm-like, skin usually without segments ; 

 legs rudimentary or reduced to tubercles or hooks ; 

 antennae none ; foot-jaws undeveloped. 



1. FAMILY. Tongue-Worms (Linguatulidse). Body 



flattened, tapering, with imbricate segments ; 



mouth with several suctorial pits containing 



as many recurved hooks. 



In this anomalous family, which is parasitic in 

 the intestines of fishes, the animal, according to the 

 researches of Van Beneden, is provided, in the young 

 state, with two pairs of jointed hooks, the nervous 

 system shews the double -knotted chord, and the 

 ovaries are bulky and internal. 



2. FAMILY. Double-Worms (Diplozoonidse). Body 



double, each half resembling the other ; 

 mouths each with two suckers ; hind part 

 of each half furnished with four membran- 

 ous expansions, each with four prehensile 

 suckers. 



This curious form of Fish-parasite is found on the 

 gills of the Bream and other fishes ; the stomach 

 is single, but each half of the body contains a dis- 

 tinct system of reproductive organs. 



3. FAMILY. Hook-tailed Worms (Gyrodactyliclse). 



