SCABIES— MANGE—SCAB 281 



cases the mites are oviparous but soMe are ovo viviparous. 

 The females lay eggs which in about eight days hatch six- 

 legged larvEe. The larvae moult forming in about three to 

 four days nymphs. Three to four days later the nymphs 

 develop to adult males and sexually mature females. The 

 females live for three to five weeks, the males about six weeks. 

 Under favorable circumstances mites may live as long as 

 eight weeks, and under contrary conditions as short a time as 

 two weeks. Infestation may be from direct contact or 

 through intermediary agents, such as harness, grooming 

 utensils, blankets, bedding, etc. 



Varieties. — ^Four varieties are distinguished : (a) Sarcoptes, 

 (6) Psoropteis, (c) Chorioptes (Symbiotes), {d) Cnemidocop- 

 tes, found only in birds. 



Sarcoptes Mite. — ^This is a burrowing parasite which lives 

 in the Malpighian layer of the skin where it forms tunnels 

 under the epidermis. It is the smallest species (0.2 to 0.5 

 mm.), shaped like the turtle, with a head like a horseshoe 

 and very short legs, the anterior two parts of which are mar- 

 ginal and the posterior two subabdominal. The males have 

 two copulatory suckers. Three varieties of sarcoptes occur 

 in animals: (a) Sarcoptes scabiei of the horse, (b) Sarcoptes 

 squamiferus of the dog, and (c) Sarcoptes minor of the cat. 



Psoroptic or Sucking. Mite. — ^This parasite lives on the 

 surface of the skin and is nourished by the blood and lymph. 

 It is the largest of the mites (0.5 to 0.8 mm.), and under 

 favorable circumstances (on black paper, for instance) may 

 be seen with the naked eye. Its head is pointed, legs very 

 long, and feet provided with tulip-shaped suckers. Two 

 varieties of this mite occur in animals: (a) Psoroptes 

 communis of the sheep and horse, and more rarely in cattle 

 and buffalo. (6) Psoroptes cuniculi of rabbits. 



Chorioptes (Symbiotes) or Scale Eating Mite. — ^This mite 

 lives on the surface of the skin and on scales of epithelium. 

 In size it stands between the Sarcoptes and the Psoroptes 

 (0.3 to 0.5 mm.) . The head is short, blunt, almost round, and 

 the legs long, provided with suckers. Two varieties belong 

 to this species: (a) Chorioptes (symbiotes) equi, bovis and 

 ovis; (6) Chorioptes (symbiotes) felis, canis and cuniculi. 



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