32 



A carology 



sists of a pit containing specialized setae (Figure 31). The Notostig- 

 mata have a similar organ and the Mesostigmata have a concentration 

 of setae on tarsus i similar to the setae of Mailer's organ. The Rhagi- 

 diidae have well-developed "Rhagidia organs" on tarsi i and ii, and 

 related groups have similar though not as highly modified structures. 



In the integument of most mites special areas consisting of pores, 

 longitudinal clefts, or depressions that are supplied by nerves or are 

 indirectly connected with the nervous system will be found. The func- 



Figiire 30 Sensillae of Trombicula 

 (Eutrombicitla) alfreddiigesi (Oude- 

 mans), 1910 and G alumna sp. 



Figure 31 A section through Haller's 

 organ of Dermacentor veniistus Banks, 

 1908. 



tion of these structures is unknown but they are probably sensory in 

 nature. Mites respond to a number of stimuli for which no organs of 

 special sense have yet been demonstrated. It is possible that these 

 obscure organs respond to such stimuli. 



Eyes are present in many of the mites and many mites that lack 

 them probably respond to changes in light intensity. The eyes of mites 

 are never developed beyond the ocellus stage. Compound eyes are 

 unknown in the Acarina. Mites that lack eyes usually have thin, trans- 

 parent areas on the dorsal surface so that changes in light intensity will 

 penetrate to the tissues below. The simplest eye consists of a concen- 

 tration of pigment granules associated with an optic nerve. The pig- 

 ment is frequently red but at times black or blue. Lenslike corneas are 

 associated with the pigment granules in many cases. The most compli- 

 cated eyes are found in certain of the water mites. Mites may have a 

 single median eye or one or two pairs of propodosomal eyes or all five 

 as is the case with many of the hydracarinids. Even the most compli- 

 cated of eyes probably do no more than detect light intensity. It is 

 doubtful that images are formed. 



