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XLII] information. It would appear that, after it has entered the human body, development is very slow, and that probably full maturity is not attained until after several years. In many cases the parasite did not show itself until 3, 4 and 4½ years after the patient had left the endemic area. In one case the parasite was extracted from the eye 13 years after the patient had left Africa; in another the worm or worms appeared at irregular intervals during 15 years. Manifestly it is long-lived. An interesting and suggestive evidence of slow development is that, while the immature active worm is often seen in children,

Fig. 158.—Chrysops dimidiata (v. d. Wulp), ♀. (Drawn by W. McDonald.)

the larval form in the blood is found as a rule only in adults. Annett, Dutton and Elliot, in 390 native children of all ages up to about 18 years, examined in a district where L. loa was exceedingly common in adults, found ''mf. loa'' once only, in a boy aged 11. Meinhof reports a case in which the period elapsing between infection with F. loa and the appearance of embryos in the blood was at least 7 years.

Slow development and a different habitat at different stages are not peculiar to L. loa only. F. equina of the horse and ass and F. labiato-papillosa of deer and cattle wander about the subdermal connective tissues and frequently occur in the eyes during their semi-adult stage, but repair to the peritoneal cavity when fully mature. The larvæ of both are found