The Filaria Sanguinis Hominis (Filaria Bancrofti), as commonly found, is the embryo of a worm that is rarely seen in the adult form. The usual form is the Filaria noctuma. The adult is from 8 to 10 cm. long and lives in the larger lymphatic vessels. No eggs are laid, but great numbers of living embryos are set free in the lymphatics and thence into the blood. The embryos are about 0.25 mm. in length, and the diameter a little greater than that of an erythrocyte. The head is broad and blunt, the tail tapering. They appear in the blood only during the period of rest. If the person works at night and sleeps during the day, they will be found during the latter period.

They escape through the kidneys into the urine in attacks of hematuria.

The mature worm, from obstruction to the lymphatics, may give rise to marked enlargements, such as lymph-scrotum and elephantiasis.

Fig. 120. - Oxyuris Ver-micularis and Egg (after Heller).

a, Natural size; b, egg.