INTERNAL PARASITES. 207 
II]. INTERNAL PARASITES (Entozoa). 
A. FIVE-MOUTHS. 
(Linguatulide.) 
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 Zongue-worm, Tonguelets or Five-mouths. According to 
the careful researches of Leuckart these parasites are simply 
degraded mites forming the order Linguatulidw. 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. Theannulated 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 
