TRACHEATA 



421 



as tlie mange or the itch. The female Sarcoptes scabei makes a 

 tunnel in the skin and sits at the inner end, pushing the eggs 

 towards the exterior as they are 

 laid. 



The Phytoptidae are gall mites, 

 and make amongst others the curious 

 conical excrescences which are so 

 common on the leaves of lime trees, 

 maples, etc. In many of them the 

 posterior pair of legs are replaced by 

 bristles. 



The Hydra-CHNIDAE or water- 

 mites are usually brightly coloured. 

 They often hang on to water-insects, 

 and may be frequently found attached 

 by their rostrum to Dytiscus, Mpa, 

 etc. One species, Atcus honzi, is 

 common in the mantle-cavity of Unio. 



The Trombidiidae are brightly-coloured mites, whose larvae 



Fig. 242. — Sarcoptes scabei (the 

 Itch Mite), female. After 

 Megiiin. 



a. Chelicerae. 



b. Pedipalpi. 



c. Head. 



Pig. UZ.— Ixodes aegyptius, Savigny. 



d. Thorax. 

 /. Abdomen. 



often live parasiticaUy on spiders or insects. Some of them, 

 as Tetrarhyncus telearius, commonly known as the red spider 



