SARCOPTID^: 517 



diseases lie dormant in winter and revive in spring and summer in man ; but in 

 animals with long wool, such as sheep, they are most active during winter, although 

 revival of active reproduction takes place in spring. 



[Speaking generally, for the Sarcoptidtz there are three distinct stages in the 

 development of the male, four in the female, as follows : 



[(i) The larva. In this stage only three pairs of legs occur. 



[(2) The nymph, in which a fourth pair of legs appear, and which thus approaches 

 the adult ; but so far no sexual organs occur. Nymphs are of two sizes the 

 smaller being future mnles, the larger females. 



[(3) The next stage in the female is the age of puberty, the female now being 

 provided with a vulvo-anal slit ; this so-called pubescent female is fertilized by the male. 

 The male then dies. But the female again casts her skin and enters another stage 



[(4) The ovigerous female the egg-laying female which has differently modified 

 legs. 



[The rate at which these Acari breed is very great. Gerlach has found that 

 roughly, in each Sarcopt gallery, a female produces fifteen individuals ten females 

 and five males and that the progeny reproduce again in fifteen days. The table 

 given below thus shows that one pair may produce the enormous number of 

 1,500,000 descendants in three months : 



First generation after 15 days ... 10 females ... 5 males 



Second ,, 30 ,, ... 100 ... 50 



Third ,, ,, 45 ,, ... 1,000 ,, ... 500 ,, 



Fourth ,, ,, 60 ,, ... 10,000 ,, ... 5,000 ,, 



Fifth ,, ,, 75 ,, ... 100,000 ,, ... 50,000 ,, 



Sixth ,, ,, 90 ,, ... 1,000,000 ,, ... 500,000 ,, 

 = 1,300,000 individuals. 



[These Acarince are divided into three distinct sub-families, namely the Cyto- 

 lichince, Sarcoptince, Canestriniince. 



[The Sarcoptin<z2\Q\\z interest us here, and of the nine genera the three following 

 are the most important : 



[(i) Sarcoptes, Latreille ; Eusarcoptes. 



[(2) Psoroptes, Gerv. ; Dermatodectes, Gerlach ; Dermatocoptes, Fiirstenberg. 



[(3) Chorioptes, Gerv. ; Symbiotes, Gerlach ; Dermatophagus, Fiirst. ; Sarco- 

 dermatocedes, Del. 



[The following are the main characters of these three genera: 



\Sarcoptes round or slightly oval; the two posterior pairs of legs being nearly or 

 quite concealed beneath the body; the tarsi end in simple long pedicles, with 

 ambulatory suckers. 



[Psoroptes oval; the legs are all visible outside the niargin of the body; the 

 ambulatory suckers are carried on long triangulated stalks ; the male has copulatory 

 suckers and abdominal prolongations. 



\Chorioptes oval ; legs long, thick, all visible ; ambulatory suckers very wide, 

 carried at the end of simple, short pedicles. 



[Sarcoptes make channels or furrows beneath the epidermis, and in these the 

 female lays her eggs. This form of acariasis is thus difficult to cure. It is the cause 

 of human itch (vide Sarcoptes scabiei). 



[Psoroptes do not make sub-epidermic galleries ; they live and breed in colonies 

 beneath crusts or scabs formed by the changes they produce in their host's skin. 

 Sheep scab is a common type of disease produced by Psoroptes. This genus is of 

 little importance as a parasite to man. 



[Chorioptes live as Psoroptes ; they also do not affect man. Otodectes, Can., 

 affecting cats and dogs, and others occur, but do not affect man as far as we know at 



