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860 human intestinal canal. In Europe the majority of cases of intestinal myiasis, a not infrequent occurrence, are caused by Fannia canicularis (a fly closely resembling the common house-fly and erroneously considered a young form of the latter on account of its smaller size), and the closely related F. scalaris. Austen believes that intestinal myiasis, due to the larvæ of these flies, is probably to be traced to the parent flies having oviposited on the anus when the patient has been using some country privy where such insects are common.

A dose of castor oil will probably suffice to expel any of these creatures that may not have been passed spontaneously.

A rational prophylaxis would consist in the covering up of food after it has been cooked, in order to prevent the access of flies.

Instances in which the larvæ have been discharged per urethram have also been met with, though more rarely.

Fig. 204.—Larva of Calliphora vomitoria.