208 INTERNAL PARASITES. 
the five-mouths resemble mites, and possess four legs, but 
when adult no external organs are visible except two pairs 
of small hooks on the head (//f), a mouth (0), and two 
minute tactile organs at the anterior border. The hooks 
can be withdrawn into little sheaths or pockets, which, with 
the mouth, make five openings in the head, hence the name 
‘‘Five-mouths.’”’ They possess no organs of vision. The 
sexes are separate; the grayish-white female, 7 to 10mm. 
long, is very much larger than the white male, which 
measures from 2 to 2.5mm. 
The Tapeworm-shaped Five-mouth (Linguatula (Pen- 
tastoma) tenioides) is illustrated in fig. 172. ‘The female de- 
posits her eggs, about 500,000, in the nasal cavities of the 
dog, fox, wolf, and other carnivorous animals, whence they 
are expelled with mucus during the fits of sneezing caused 
by their presence, and in this manner they reach the surface 
of various low-growing plants or water. Protected by the 
mucus they keep alive for a number of weeks. If the plants 
coated with such eggs are eaten by any herbivorous animal, 
the mucus and egg-shells are dissolved, and the embryos, 
which were fully formed when the eggs were laid, are liberated 
in the intestines of the new host. The embryo is flat on the 
lower, round on the upper surface, and constricted and den- 
tated at the posterior end. In this larval shape it bores 
through the walls of the digestive tube by means of a per- 
forating apparatus formed by a style with two hooks, and 
thus reaches the liver, lungs, etc., where it becomes encysted. 
Here it gradually assumes the pupal shape. During thenext 
five months a number of moults take place, and the body of 
this secondary larva becomes elongated, broader in front, 
and is divided into 80 tc 90 segments, which possess a series 
of fine points on their posterior borders. (Fig. 172). To- 
wards the seventh month these larve are completely de- 
veloped, measuring from 6 to 8mm., and now leave their old 
home. Most of them die in their attempts to reach the nasal 
cavities of a new host, but some succeed. Dogs that eat the 
viscera of animals containing these parasites are certain to 
become infested with them. At all events the larve must 
reach respiratory organs to complete their growth, which 
