OF THE CLASS AEACHNIDA. 



421 



the blood. Some are without eyes, and in those which have 

 them, we never find more than two or four. Some of these 

 animals, known by the name of faucheurs, greatly resemble 

 spiders, and are remarkable for the length of their limbs ; 

 others have the mouth formed for suction, and constitute the 

 family acari or mites ; they are very small, and several live 

 as parasites on other animals. 

 One species, the ixodes of Brazil, 

 fixes itself on dogs, oxen, &c., 

 and so deeply plunges its suckers 

 into the flesh of these animals, 

 that they cannot be detached 

 without raising up the portion 

 of the skin to which they adhere. 

 It is asserted that the multipli- 

 cation of these parasites is some- 

 times so considerable as to cause 

 the death of the oxen and horses 

 to which they have fixed them- 

 selves, by exhaustion.* Another 

 kind of mite, called leptus au- 

 tumnalis, or rouget, is very com- 

 mon in the autumn in our fields, 

 and, insinuating itself under the 

 skin of the legs, causes in- 

 supportable itchings. Finally, 

 it is a small animal of this 

 family which, by multiplying in winding burrows under the 

 skin, occasions one of the most disgusting diseases, the Psora or 

 Itch. The sarcopt of the Psora (Fig. 417) is scarcely visible to 

 the naked eye; but when examined with a microscope, its body 

 is seen to be oblong, and its mouth to have the form of a 

 conical papilla armed with several bristles, and its feet, 

 eight in number, differ very much from each other, the four 

 posterior feet being terminated only by bristles, whilst tin- 

 four anterior feet are furnished at their extremity with small 

 suckers, by means of which they can adhere to the most 

 polished bodies. 



* Parasitical animals of this class abound in Southern Africa, and I am 

 aware that they attach themselves indiscriminately to oxen, horses, dogs, 

 &c., but it seemed to me that they had a predilection for the diseased or 

 enfeebled animal ; for if by chance an exhausted horae was left on the Held 

 for some days, he became covered with these vermin, whilst they seldom 

 attached themselves to the healthy, well-fed animal. E. K. 



Fig. 417. Sarcopt of the Psora 

 (magnified). 



