112 ACAKINA OR MITES. 



given rise to six generations, is accountable for 1,500,000 

 individuals in about ninety days. 



The Sarcoptes have a rounded body. The posterior legs are 

 very small, and nearly or quite concealed beneath the body. The 

 ambulacral sucker is in the form of a simple long pedicle. The 

 females deposit their eggs at the bottom of the furrows they 

 excavate in the sub-epidermic tunnels. Psoroptes have a more 

 oval body, aU the legs are visible, and the ambulatory suckers 

 are borne on large three-jointed pedicles. The psoroptes do 

 not make sub-epidermic galleries, but live in societies amongst 

 the crusts they cause on the skin. SymMotes are oval, and have 

 all the legs visible outside the body margin, with the claws 

 borne on a broad, short, and simple pedicle. These live like 

 psoroptes in colonies under the scabs, and cause more localised 

 patches than the others. 



Each domestic animal has a variety common to it ; but it is said 

 that the itch of man can be taken by the dog and other animals, 

 a point which cannot be accepted as invalid. The sarcoptic 

 mange of the horse, however, can be easily transmitted to the 

 ox. Regarding the transmission from one animal to another and 

 man, there is much diversity of opinion. 



Sheep-scab. 



The Scab or Soab of sheep is of three types, produced by the 

 three genera of Sarcoptidce. The commonest form of scab is 

 that produced by Psoroptes communis v. oms. It is sometimes 

 called Demodectic Scabies. The acarus can be seen with the 

 naked eye, and may readily be found under one of the scabs 

 in all stages. The female Psoropt of the sheep has a large 

 round body with four pairs of short legs, the third and fourth 

 pairs being of nearly equal size ; but the third is devoid of the 

 curious sucker on the feet. The male has the fourth pair of 

 legs very short, the third pair being long, and armed with 

 the sucker. The ova laid by the female are comparatively 



