424 



PHYLUM ARTHROPODA 



(c) With or without trachcce. In Acarapis woodt, parasitic in the 



thoracic tracheas of hive-bees suffering from Isle of Wight 



disease, the female breathes by trachea^, the male simply by 



the skin. 



Ticks (Ixodida?, etc.) are the largest Acarina. They show a movable 



" capitiilum " bearing serrated cutting chelicercT? and strong four-jointed 



pedipalps. They are responsible for spreading the germs of some 



diseases affecting man and beast, e.g. hum.an " tick-fever " on the 



Congo, spread by Ornithodoros mouhata ; a spirochaete disease in poultry, 



borne b}^ Argas reflexus and A. persicus ; Texas fever or " red water " 



in cattle, carried by Boophilus annulatus. The common sheep-tick in 



Fig. 236. — Tick {Ixodes riduvius, 

 female), dorsal surface, showing the 

 oval shield (S//.).— After Wheler. 



H., Hypopharynx ; P., palp L.I., L.IV., 

 first and fourth leg. 



Fig. 237. — Tick {Ixodes riduvius, 

 female), ventral surface. — After 

 Wheler. 



R., Rostrum ; P., palp ; G., genital 

 aperture; ST., stigma ; /I. , anus. 



Britain is Ixodes ricinus. It may be noted that mites have been found 

 inside human tumours, and there are many facts suggesting that some 

 of the small Acarines may share in spreading disease germs. Even 

 Deviodex may play its part. 



Aberrant Orders 



Order Linguatulida or Pentastomida, e.g. Pentastomum 



tcenioides 



This strange animal is parasitic in the nasal and frontal cavities, etc., 

 of the dog and wolf. It is worm-like in form, externally ringed. 



