PARASITES OF ANIMALS. 17 
animals, and run with agility either forward, sideways, or 
backward, somewhat like a crab. Their feet or tarsi are fur- 
nished with powerful denticulated claws, with which they 
cling securely. Their most remarkable peculiarity is their 
mode of reproduction. Hach female produces but one or two 
young at a time, but these are born as living, fully developed 
larve, which are enclosed in a smooth oval skin, notched at 
one end, within which they change to pupe immediately 
after birth, the enclosing case becoming dark colored. The 
female has an uterus-like enlargement of the oviduct, in which 
the eggs hatch, and this organ has the power of secreting a 
milk-like substance for the nourishment of the larve until 
full grown. 
The Horse-tick or Forest. -fly (Hippobosca equina). Figure 20. 
This species is alnaost as large as the house-fly, nearly black, 
with conspicuous yellow markings on the thorax. It some- 
Figure 20. 
times infests the horse 
to such an extent as to 
b | / ZEB be very troublesome. 
We EA It attacks by prefer- 
ence those aes re 
the hair is thinnest 
and the skin softest, 
especially under the 
al ; belly and between the 
: hind-legs. Their bites 
cause severe pain, and will irritate the gentlest horses, often 
rendering them almost unmanageable, and causing them to 
kick dangerously. When found they cling so firmly as to be 
removed with some difficulty, and they are so tough as not to 
be readily crushed. If one escapes when captured, it will in- 
stantly return to the horse, or perchance to the head of its 
captor, where it is an undesirable guest. Another species 
sometimes infests the ox. 
Figure 20.— The Horse-tick (Hippobosca equina Linn.), enlarged. From 
Cuvier. 
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