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782 ''mf. loa'' is often disposed in a series of sharp flexures, giving it in some instances a corkscrew-like appearance, the extreme tip being always sharply flexed. (Plate XI., Fig. 6.) (3) The nuclei of the central column of cells of ''mf. loa are larger and stain less deeply than those of mf. bancrofti'', and, as a rule, the cephalic end of the column is more abruptly terminated in the former. Although in most slides one or two specimens may be hard to diagnose, on the average of a series of preparations the foregoing distinctions are recognizable. Fülleborn by special staining methods points out various minor differences (see Fig. 98), amongst which the large genital cell is a marked feature. He proposes the measurement of various fixed points (Fig. 128) as a standard of differentiation of the various microfilariæ.

Life-history.—Of the life-history of L. loa little is positively known. As the larval form comes into the peripheral

circulation of the human host, it is very probable that, like mf, bancrofti, it is liberated by some blood-sucking insect; and, seeing that it approaches the surface of the body only during the day-time, this is undoubtedly a blood-sucker of diurnal habit.

Several years ago I called attention to the so-called mangrove flies as possible intermediaries, specifying as the most probable Chrysops dimidiata (Fig. 158). This conjecture Leiper has ascertained to have been well founded. During a recent visit to West Africa, with the object of ascertaining the intermediary host of L. loa, he examined many blood-sucking insects, including mosquitoes and a variety of other insects. He found that in Chrysops dimidiata and in C. silacea rapid and uniform developmental changes of ''mf. loa were effected, similar to those of mf. bancrofti'' in the mosquito. Later observations by Kleine, working in the Cameroons, tend to confirm those of Leiper. As to the way in which L. loa is acquired we must await further