PHYLUM ARTHROPODA. 



Congo, spread by Ornithodoros moubata ; a spirochset disease in poultry, 

 borne by Argas reflexus and A. persicus ; Texas fever or " red water " in 

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



FlG. 197. Tick (Ixodes riduvius, 

 female), dorsal surface, showing the 

 oval shield (SH.\ After Wheler. 



ff. t Hypopharynx ; P., palp ; L.7., L.IV., 

 first and fourth leg. 



FIG. 198. Tick (Ixvdes riduvius, 

 female), ventral surface. Aftei 

 Wheler. 



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

 aperture; ST., stigma; /4.,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 

 Demodex may play its part. 



t 

 Aberrant Orders or Classes 



Order LINGUATULIDA or PENTASTOMIDA, e.g. Pentastomum 

 tanioides 



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, 

 without any oral appendages, but with two pairs of movable hooks near 

 the mouth. The muscles are striated. The alimentary canal is very 

 simple, without Malpighian tubes. A narrow circumcesophageal nerve- 

 ring, without a brain, is connected with a single ventral ganglion. 

 There are no sense organs nor tracheae, nor is there any heart. The 

 sexes are separate ; the males smaller than the female. 



Embryos within egg-cases pass from the nostrils of the dog. If they 

 happen to be swallowed by a rabbit or a hare, or it may be some other 

 mammal, the embryos hatch in the gut and penetrate to liver or 



