268 



ARTHROPODA 



Order III. Acarina. 



[CH, 



The Acarids (Gk. d/cu/ae's, a morsel) or Mites form an enormous 

 order whose function in life is to a large extent to play the 

 scavenger, and the terrestrial forms confer the same benefits on the 

 dwellers on the Earth that the Ostracoda and many of the smaller 

 Crustacea do on the aquatic fauna. Many of them however have 

 adopted parasitic habits and cause disease amongst larger animals, 



FIG. 121. Tyroglyphus siro, seen from the ventral side. A. Female. 

 B. Male. Magnified. From Leuckart and Nitsche. 



1. Pedipalpi. 2. Chelicerae. 3, 4, 5, 6. First, second, third and fourth 

 walking legs. 7. Chitinous thickenings supporting legs. 8. Furrow 

 round body. 9. Eeproductive opening, flanked by two suckers on each 

 side. 10. Anus. 11. Suckers at side of anus. 



while some induce the formation of galls and other deformities 

 amongst plants. Most of the Mites, as their name indicates, are of 

 minute size ; but the female Ticks, belonging to the family Ixodidae, 

 which live amongst the undergrowth of forests on the look-out for 

 some vertebrate prey, when they become attached to their hosts 

 man, cattle, or even snakes can, by distending their bodies with 

 the blood they suck, swell out to the size of hazel-nuts. 



Anatomically Mites are difficult to characterise. Like the 

 Phalangids, they have no waist, and when special breathing organs 

 are present they take the form of tracheae ; they differ however 

 from the Phalangids in never showing signs of segmentation. The 



