CHAPTER XIX. 



THE ARACHNOIDS. 



Order. 



Acarina, 



CLASSIFICATION OF THE ARACHNOIDEA. 



Family. Subfamily. ' Genus. Species. 



Trombidiidae, Trombidium, T. holosericeum. 



Gamasidae, Dermanyssus, D. gallinae. 



Tyroglyphidae, TV!!,,,* / T - f arinae > 



T. longior. 



Sarcoptidae, 

 Demodicidae, 



Ixodidae, 



Linguatulida, 



Sarcoptes, 

 Demodex, 



Argas, 



Ornithodoros, 

 Ixodes, 

 Hyalomma, 

 Rhipicephalus, 



Dermacentor, 



Margaropus, 

 Amblyomma, 

 Haemaphysalis, 

 f Linguatula, 

 \ Porocephalus, 



THE ARACHNOIDEA. 



Argasinae, 



Ixodinae, 



S. scabiei. 



D. folliculorum, 



A. persicus. 



A. miniatus. 



O. saviguyi. 



I. ricinus. 



H. aegyptium, 



R. bursa. 

 f D. reticulatus. 

 \ D. andersoni. 



M. annulatus. 



A. hebraeum. 



H. leachi. 



L. rhinaria. 



P. constrictus. 



The Archnoidea differ from the Insecta in having the head and 

 thorax fused together. They also have 4 pairs of ambulatory ap- 

 pendages, while the insects only have 3 pairs. The Arachnoidea never 

 have compound eyes these when present being simple. Of the 2 

 orders of Archnoidea of interest medically the Acarina is far more 

 important than the Linguatulida. 



ACARINA. 



Of the acarines we are chiefly interested in the mites and the ticks. 

 The acarines do not show any separation of the abdomen from the 

 cephalo-thorax. A hexapod larva develops from the egg; this is 

 succeeded by an octopod nymph which differs from the adult in not 

 having sexual organs. 



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