_Tyroglyphus siro_ is a small mite of a whitish color. The male measures about 500µ long by 250µ wide, the female slightly larger. They live in cheese of almost any kind, especially such as is a little decayed. "The individuals gather together in winter in groups or heaps in the hollows and chinks of the cheese and there remain motionless. As soon as the temperature rises a little, they gnaw away at the cheese and reduce it to a powder. The powder is composed of excrement having the appearance of little grayish microscopic balls; eggs, old and new, cracked and empty; larvæ, nymphs, and perfect mites, cast skins and fragments of cheese, to which must be added numerous spores of microscopic fungi."--Murray. _Tyroglyphus siro_, and related species, have been found many times in human feces, under conditions which preclude the explanation that the contamination occurred outside of the body. They have been supposed to be the cause of dysentery, or diarrhœa, and it is probable that the _Acarus dysenteriæ_ of Linnæus, and Latreille, was this species. However, there is little evidence that the mites cause any noteworthy symptoms, even when taken into the body in large numbers. _Histiogaster spermaticus_ (fig. 152) is a Tyroglyphid mite which was reported by Trouessart (1902) as having been found in a cyst in the groin, adherent to the testis. When the cyst was punctured, it yielded about two ounces of opalescent fluid containing spermatozoa and numerous mites in all stages of development. The evidence indicated that a fecundated female mite had been introduced into the urethra by means of an unclean catheter. Though Trouessart reported the case as that of a Sarcoptid, Banks places the genus _Histiogaster_ with the Tyroglyphidæ. He states that our species feeds on the oyster-shell bark louse, possibly only after the latter is dead, and that in England a species feeds within decaying reeds. _Nephrophages sanguinarius_ is a peculiarly-shaped, angular mite which was found by Miyake and Scriba (1893) for eight successive days in the urine of a Japanese suffering from fibrinuria. Males, .117 mm. long by .079 mm. wide, females .36 mm. by. 12 mm., and eggs were found both in the spontaneously emitted urine and in that drawn by means of a catheter. All the mites found were dead. The describers regarded this mite as a true endoparasite, but it is more probable that it should be classed as an accidental parasite. MYRIAPODA There are on record a number of cases of myriapods occurring as accidental parasites of man. The subject has been treated in detail by Blanchard (1898 and 1902), who discussed forty cases. Since then at least eight additions have been made to the list.