The worm inhabits the lung of the frog and toad, and is hermaphrodite (Schneider) or parthenogenetic (Leuckart); the embryos hatched from the eggs find their way through the lungs into the alimentary canal and thence to the exterior; in a few days they develop into a sexual larva, called a Rhabditiform larva, in which the sexes are distinct; the eggs remain within the uterus, and the young when hatched break through its walls and live free in the perivisceral cavity of the mother, devouring the organs of the body until only the outer cuticle is left; this eventually breaks and sets free the young, which are without teeth, and have therefore lost the typical Rhabditis form.
Bancrofti is known to live in the lymphatic glands, and its embryos Microfilaria sanguinis hominis nocturna, passing by the thoracic duct, reach the blood-vessels and circulate in the blood.
The eggs of the female give rise to embryos within the body of the mother; her other organs undergo a retrogressive change and serve as food for the young, until the body-wall only of the mother remains as a brown capsule.
The sub-umbral cavity (s.c.) functions as a brood-space for the developing embryos, which are set free by rupture of the wall.
The fertilized egg-cell (oospore) forms a filamentous structure, the proernbryo, from a restricted basal portion of which one or more embryos develop, one only as a rule reaching maturity.