INTERNAL PARASITES. 207 



II. INTERNAL PARASITES (Entozoa). 

 A. FIVE-MOUTHS. 



( LingvatididcE.') 



Among the many parasites infesting man, domesticated 

 animals, certain wild animals, and even amphibians, few are 

 more degraded in consequence of a parasitic mode of life than 

 the Tongue-ivorm, Tonguelets or Five-mouths. According to 

 the careful researches of Leuckart these parasites are simply 

 degraded mites forming the order Liiujuatididw. This com- 

 prises arthropods with elongated, worm-shaped and annu- 



Fig. 172. — Five-mouth. To the left, secondary larva; in center, 

 male, and below a single hook; to the right, a female. Greatly en- 

 larged. After Brass. 



lated bodies, possessing mouths without jaws, and which 

 are surrounded by two pairs of hooks representing rudi- 

 mentary legs. In the adults these parasites possess no 

 hearts, and breathe through their skins. The annulated skin 

 contains numerous glands of uncertain use. The ventral 

 mouth, surrounded by a chitinous ring, opens into a central, 

 straight, intestinal tube ending at the posterior end. The 

 illustration (fig. 172) shows this peculiar parasite, and indi- 

 cates also why it "was not so very strange that formerly it 

 ■was considered a tremadode-worm or a fluke. When young 



