50 



Arachnida and Myriopoda 



removed, and in such cases the irritation and itching persist for 

 several weeks. 



Dermacmtor occidentalis is called the Pacific Coast Tick or 

 Wood Tick. The habitat of this species is the Pacific coast-region 

 of the United States (Coast Eange and Sierra Nevada Mountains 

 in California and Oregon, and the smaller mountain-ranges in 

 south-western California). It is found on cattle, horses, human 

 beings, deer, dogs, etc. 



Dermacmtor variabilis, Say. 



This North American dog-tick sometimes attacks human beings, 

 but apparently without causing ill effects of any consequence. 



It is usually found on the dog, but occasionally on other 

 animals. 



Genus — Ixodes, Latreille. 



Ixodes ricinus, Linnaeus. 



Inflammation and other ill effects are said to result sometimes 

 from the bite of Ixodes ricinus, L., but such cases are rare; the 

 bite of this tick usually only sets up a certain amount of irritation, 

 and there are no serious consequences. 



Specimens of Ixodes, usually I. ricinus, sometimes, however, 



occur in tumours under the skin 

 of human beings, and similar 

 cysts, each containing a tick 

 belonging to this genus, have 

 also been found in the skin of 

 horses, cattle, dogs, and foxes. 

 Cases of this kind are, however, 

 of quite an exceptional nature. 

 It is supposed that the irritation 

 caused by the hypostome of the 

 Ixodes sets up inflammation 

 and swelling of the tissues, 

 which gradually envelop the 

 parasite. The external wound 

 may heal, leaving only the 

 internal cyst enclosing the tick. 

 The bite of Ixodes ricinus is 

 reported by Dubreuille to have 

 caused a gangrenous pustule, 



Fig. 24. 



Ixodes ricinus, L. Female. 

 Enlarged. 



