156 Veterinary Medicine. 



tion of 50 in 15 days ; about 730,000,000 from one pair in three months. Vi- 

 tality : Least in Sarcoptes, greatest in Symbiotes, and especially in Pso- 

 roptes. Divisions : Sarcoptes, burrowing acari ; psoroptes, surface acari on 

 body ; symbiotes, surface acari on limbs. List of psoric sarcoptidse. 



These stand apart from the other acari mainly in their tendency 

 to cause a dermatitis accompanied by intolerable itching from 

 which the various names of the affections have been derived : 

 Greek, Pso I rub ; Latin, Scabere to scratch ; Italian, rogna, 

 raspa ; Spanish, sarna, rona ; German, kratze ; French, gale ; 

 English, itch, scab, scald, mange (manger to eat). 



They have the common characters of a flattened body, sym- 

 metrically striated, with dermic plates (plastrons). The feet are 

 furnished with cushions or bell shaped suckers. The four pos- 

 terior limbs differ from the anterior, and in the females, nymphae 

 and larvae, and in some cases in the males, the cushions are re- 

 placed by long hairs. Megnin further credits them with a 

 venomous saliva which serves to produce itching and dermatitis. 

 The rostrum of variable size in different species, is conical and 

 mobile, formed of maxillse and labiae united and two chelicera 

 and one lancet shaped tonguelet free. The male organs, between 

 the two last limbs show a number of chitinous plates, and two 

 lateral symmetrical suckers which fix on the body of the female. 

 The vulvo-anal .slit on or just above the posterior border, enlarges 

 greatly about the period of breeding. The male has four testicles, 

 two on each side, the excretory ducts of which join in a single 

 canal in the penis. The female has but one ovary and oviduct 

 ending in a cloaca. They are oviparous, the eggs hatching out 

 in from 3 to 10 days, or in favorable conditions in 24 hours. 

 The metamorphoses are the same as in other acari : 



1 . Larva. Hexapod ; asexual ; small ; it passes through 

 two or three moultings becoming on each occasion a simple cel- 

 lular mass in which, as in an impregnated ovum, the elements of 

 the new being are developed. 



2. Nympha. In the last moulting a fourth pair of legs is 

 developed, but no sexual organs, the males and females being 

 distinguished by their smaller and larger size. 



3. Mature Male and Female. From the moulting, which 

 terminates the stage of nympha, the acari emerge with distinct 

 male and female sexual organs. Copulation takes place, the 



