in length by 0.0045 mm. in breadth; but, as it possesses in a remarkable degree the power to elongate and to shorten itself, these measurements do not always apply. It is manifestly much smaller than mf. bancrofti and mf. loa, and is further distinguished from these microfilariæ by the entire absence of a sheath, and by the characters of its caudal end, which is invariably truncated and abruptly rounded off. The taper which terminates in the tail extends through quite two-thirds of the entire length of the animal. Further, if the head be carefully observed with a high power, a fang can generally be easily seen— much more easily than the corresponding structure in mf. bancrofti— in constant play, shot out and retracted. The V spot is about 0.03 mm. from the cephalic extremity. There is no marked tail spot. No hooked cephalic prepuce can be made out. According to Fülleborn, no red staining " granular mass " can be demonstrated as in the case of mf. bancrofti and mf. loa. Its movements also differ from those of mf, bancrofti, for it not only wriggles about, just as that parasite does, but it indulges in long excursions through the blood, moving freely all over the slide, locomoting in fact very much in the same way as mf. bancrofti does in the mosquito's stomach after it has cast its sheath.
Adult form.— The adult form, discovered by Daniels in Demerara Indians, and subsequently identified by myself as that of F. perstans, is, like F. bancrofti, a long, cylindrical filiform nematode. The body is smooth, without markings; the mouth simple and unarmed. The tail in both sexes is peculiar and characteristic; it is incurvated, and the chitinous covering at the extreme tip is split up as it were into two minute triangular appendages, giving it a mitred appearance (Fig. 127). The adult female measures 70 to 80 mm. in length by 0.12 mm. in breadth. The head is club-shaped and measures 0.07 mm. in diameter. The genital pore opens at 0.6 mm. from the head. The anus opens at the apex of a papilla situated in the concavity of the curve formed by the tail. The diameter of the tail just before termination is 0.02 mm. The male is smaller than the female; it measures 45 mm. in length by 0.06 mm. in breadth. The diameter of the head is 0.04 mm. Close to the opening of the cloaca there are four pairs of preanal and one pair of postanal papillae, and, according to Leiper, another small pair are situated midway between these groups. Two unequal spicules may sometimes be seen protruding from the cloaca. So far the adult forms have been found only in the connective tissues at the root of the mesentery, behind the abdominal aorta, and beneath the pericardium.
Life-history.—Very little is known of the life-history of F. perstans. Although it has a wide geographical range, this filaria appears to be limited in its topography to areas covered by dense forest growth and abounding in swamps. In Kavirondo, where the forest disappears and the land is covered with scrub and short grass, it is not found; likewise it
