ACAKINA OE MITES. Ill 



such as " louping-ill " ^ and Texas Fever in sheep and cattle 

 respectively. 



Family Sarcoptidae. — These minute mites live as parasites in 

 and upon animals and man. The body is round or oval ; in 

 front is a conical rostrum. The sexes are told by the differences 

 in the legs and general shape of the body and by the size, the 

 male being always much smaller than the female. They occa- 

 sion diseases that are spoken of as Scabies or Psoric diseases. 

 The Sarcoptidaj are the smallest of all mites, varying from •1mm. 

 to 1mm. (JL- inch) in length. No eyes are present, and respira- 

 tion is cutaneous. The Psoric Sarcoptidas attack the epidermis of 

 animals, and the punctures they produce, with the addition of a 

 poisonous saliva, give rise to thick crusts over their point of 

 attack. The Sarcoptidae are oviparous and ovoviviparous. The 

 eggs are slightly ovoid, and the contained embryo is easily seen 

 in an ovum in an advanced stage. The eggs incubate in a few 

 days. In some cases the author has observed the ova to hatch 

 in two days in the species producing Sheep Scab ; more usually 

 seven to ten days is the period. 



The metamorphosis is as follows : — 



The Larval or first stage is a small acarus with only three pairs 

 of legs and no genital organs, and with two long anal bristles. 

 The larva moults two or three times. Then follows the second 

 or Nympli stage. The nymph has a fourth pair of legs, which 

 are, however, small. As yet no sexual organs are to be found. 

 We observe two sizes of nymphs ; the small ones will be males, 

 the large females. Casting their skin, both males and females 

 are produced, and now copulation takes place. They are then 

 known as j^f-bescent males and females. The male then dies ; 

 hut the female undergoes another moult, and becomes the 

 ovigerous female, with a sub -thoracic vulva, which deposits 

 about 15 large ova. Gerlach states that one female, having 



' The exact part they play in " louping-ill " is not known ; but the 

 evidence of Professor Williams and others shows clearly that the Tick is 

 connected with this fatal disease. 



