The sexual form of _Mermis nigrescens_ Duj.[187] lives in damp earth, and after storms and in the early morning is sometimes found in such numbers crawling up the stalks of plants, as to give rise to the popular idea that there has been a shower of worms. The male is unknown; the female lays her eggs in the ground, and there they hatch out. It is not known exactly how the larvae make their way into the grasshoppers in whose body-cavity they live, but in an allied species, _M. albicans_ v. Sieb., the larvae have been observed boring their way into small caterpillars through their skin, and it seems probable that the larvae of _M. nigrescens_ burrow in a similar way into young Orthoptera. _Bradynema rigidum_ Leuck.[188] is found in the adult stage living freely in the body-cavity of a small beetle _Aphodius fimetarius_, one of the Scarabeidae, from two to three to as many as thirty being found in one host, which does not seem much injured by their presence. The parasite is without mouth, anus, or excretory pore. The eggs hatch out in the uterus of the mother, and the larvae are male and female; they make their way into the body-cavity of the host, and here they pass an unusually long time, five months, soaking in osmotically the nutriment contained in the blood of the insect. Eventually they burrow through the walls of {151}the intestine, and leaving the body of their host through the anus, find their way to the earth. Here, according to zur Strassen, the females die without playing any part in the perpetuation of the species. The males, on the other hand, having developed spermatozoa whilst in the larval stage (paedogenesis), afterwards form ova, and are in fact protandrous hermaphrodites, and become the mature parasites of the beetle, though how they enter the body of the host is unknown. [Illustration: FIG. 74.—_Allantonema mirabile_ Leuck. (From Leuckart.) A, Male Rhabditis stage, sexually mature, × 100; B, the mature female parasitic form, × 17, showing at the upper end part of the capsule richly supplied with the tracheae of the host, a beetle; C, female Rhabditis stage, sexually mature, × 100; D, the larva developed from the Rhabditis form, × 102.] The phenomenon presented by the hermaphroditism of _Bradynema_ is, as far as we know, at present unique, as, though some other Nematodes are hermaphrodite, in their case the hermaphrodite form alternates with a bisexual generation. It is further interesting as showing a means by which hermaphroditism may arise, by the suppression of the females and the assumption of their functions by the male. In the case of _Rhabdonema nigrovenosum_, no females appear in the alternate generation. {152}[Illustration: FIG. 75.—_Atractonema gibbosum_ Leuck. (From Leuckart.) 1, Female with commencing prolapsus of the uterus and neighbouring parts, × 130; 2, a further stage, the female being now sexually mature, × 15; 3, a still older stage, with commencing degeneration of the body of the female, × 15.]