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. Each female produces but one or two 

 young at a time, but these are born as living, fully developed 

 larvae, which are enclosed in a smooth oval skin, notched at 

 one end, within which they change to pupae 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 larvae until 

 full grown. 



The Horse-tick or Forest-fly (^Hippobosca equina). Figure 20. 



This species is almost as large as the house-fly, nearly black, 

 with conspicuous yellow markings on the thorax. It somc- 

 ^^&^^^^- times infests the horse 



to such an extent as to 

 be very troublesome. 

 It attacks by prefer- 

 ence those parts where 

 the hair is thinnest 

 and the skin softest, 

 especially under the 

 belly and between the 

 hind-logs. 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 {Eippobosca equina Linn.), enlarged. From 

 Cuvier. 



