546 ARACHNIDA ORDERS ACARINA AND TARDTGRADA. 



In Brazil they are said to have been introduced. This has been doubted ; 

 but it is not unlikely that a particularly troublesome species may be carried 

 from one country to another, or introduced into districts in which it was pre- 

 viously unknown. For a tropical country, Jamaica is remarkably free from 

 noxious creatures ; and it is only of late years that ticks have multiplied in 

 the island to such an extent as to make it highly unpleasant to venture 

 among the herbage at all. This is attributed to the introduction of the 

 mongoose, which was imported to destroy rats, and which is said to have 

 carried the ticks over the whole island. The largest known ticks, which 

 sometimes attain a length of nearly an inch, are those which are found occa- 

 sionally upon the tortoise. Argas persicus (Fisch.) was said by travellers to 

 produce fatal injuries by its attacks, and to abound so much in some parts of 

 Persia as to lead to the abandonment of whole villages ; but these reports 

 are now believed to have been much exaggerated. 



The Oribatidce are dark-coloured, hard, shiny mites, found among moss 

 and vegetable refuse ; but when they are older, they feed on various small 

 insects. The front of the body is often produced into a broad, triangular 

 shape, and, as in many other mites, the palpi are frequently so largely 

 developed as to resemble antennae in appearance. 



The Phytoptidce, or gall mites, are an extremely large group, concerning 



which much has been written of late years. They are very long, microscopic 



mites, usually with only four legs visible at the anterior end 



Gall-Mites of the body. They produce small galls on the leaves of 



(Phytoptidce). various plants, sometimes conical, as on the lime trees, and 



sometimes rounded, as on the vine. These galls may be 



distinguished from insect-galls by having a small opening at the base. 



The Sarcoptidcv, or itch-mites, are a family of parasites which, not content 

 with sucking blood, burrow under the skin of warm-blooded animals, causing, 

 by their irritation, diseases known as the itch or mange. 

 Itch-Mites Various species have also been observed on patients suffering 

 (Sarcoptidce). from Polish Plait (Plica polonica), and whether they actually 

 cause this disease or not, they doubtless aggravate it. The 

 itch-mites are round, with short, bristly legs, and most mammals seem to be 

 more or less subject to their attacks. In birds, they frequently attack the 

 feet. They are most active at night, and the 

 troublesome itching they cause is consequently 

 worst then. There are two principal forms of 

 the disease in man, one common in most parts of 

 the world, caused by Sarcoptes scabiei (Latr.), while 

 the other, S. scabiei-crustosce (Murray), which is far 

 worse, is almost confined to Northern Europe. The 

 itch has often been a great pest during the hard- 

 ships of a campaign, and the survivors of Sir John 

 Moore's force, in the Peninsular War, were greatly 

 affected by it. Before the cause was discovered, it 

 was regarded as a most formidable disease, and Dr. 

 Russell informs us that in the last century it was more 

 dreaded at Aleppo than the plague itself. But in 

 Fig 20. TTCH-MITE recent years, the use of sulphur baths has proved 



\Sarcoptes scabiei). Under- , , -, 2 J.T j * -. -i 



surface of male. Magnified. to be an easv and emcacious method of getting rid 



of at least the milder forms of this complaint. 

 Two other families of parasitic mites may be briefly mentioned. These 



