. The Acarina or mites. A review of the group for the use of economic entomologists. Mites. 94 EEPORT 108, U. S. DEPARTMENT OF Fig. lS5.—0ribatella armata. (Author's illustration.) and that this is the bursa copulatrix. Coition, however, has not been observed, so it is not certain that the male does not use the vagina. The tracheae when present vary much in shape and size. They open at the acetabula of the legs; one or two tra- cheae proceed from each ace- tabulum ; sometimes they are verylongand wind about in the body; sometimes short, and again they may be enlarged to form air
. The Acarina or mites. A review of the group for the use of economic entomologists. Mites. 94 EEPORT 108, U. S. DEPARTMENT OF Fig. lS5.—0ribatella armata. (Author's illustration.) and that this is the bursa copulatrix. Coition, however, has not been observed, so it is not certain that the male does not use the vagina. The tracheae when present vary much in shape and size. They open at the acetabula of the legs; one or two tra- cheae proceed from each ace- tabulum ; sometimes they are verylongand wind about in the body; sometimes short, and again they may be enlarged to form air sacs. In HopJoderma there are no tracheae and in Nothrus they are rudimentan.', and they are lacking in the larvae and nymphs of all forms. There are various excre- tory organs; one pair, the supercoxal glands, open near the acetabula of the second legs; others, the expulsory v'esicles, open on the sides of the abdomen. The Oriba- tidae have a delicate sense of touch, which re- sides apparently in the long hairs or setae upon the legs, particularly a very long hair on the tibia. They have no eyes, yet have a quick ap- preciation of light and darkness, and prefer the latter. It is quite possible that the pseudo- stigmata are organs of hearing. The food of the Oribatidae is usually of a vege- table nature, but a few species affect decaying animal matter; one of our common species is usu- ally found on bones. Many feed on lichens and fungi, and some bore into decaying wood. Sev- eral kinds are found on the bark of liA-ing trees, and others under dead bark. Many species oc- cur in moss, but do not necessarily feed upon it. None of them is parasitic in any stage. Most species are slow in traveling, and often, when disturbed, feign death. Some of the adult mites, as stated, carry their molted skins and other rub- bish on their backs. Practically none of the Oribatidae is of eco- nomic importance. A few have been recorded as damaging grass, and one {Lia~ carus cnpitatvs Banks) occur
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