E. Gordiidae

Very long thin worms similar to Filariæ, which, in their adult condition, live free in brooks, pools and springs; the mouth and the commencement of the intestine are obliterated; there are no lateral ridges, and the muscular system presents a structure different to that of the Nematoda. The posterior end of the male is split, and spicules are lacking; there are two testicles. In both sexes the genitalia discharge through the terminal gut.

The larvæ, which carry a rostrum beset with hooks, force themselves into the larvæ of water-insects; more rarely they invade molluscs, and they then become encysted within the body of the host. According to Villot, at least a part of them attain the intestine of fishes, where they again become encysted, and after a period of rest they travel into the tissues of their hosts, and finally again reach the exterior by way of the intestine, where they then become adult. In most cases, however, the gordius larvæ are taken up by predacious water insects; they live for a while in the body cavity of these insects, undergo a metamorphosis, and finally wander into the water.

A few species invade man accidentally with water, in which case they are usually vomited up:—

Gordius aquaticus, Dujardin, 30 to 90 cm. in length (Aldrovandi, Degland, Siebold, Patruban).

Gordius tolosanus, Duj., 11 to 13 cm. in length (Fiori).

Gordius varius, Leidy, 10 to 16 cm., female, up to 30 cm. in length (Diesing).

Gordius chilensis, Blanch. (Guy). Gordius villoti, Rosa (Bercutti, Camerano); Gordius tricuspidatus, L. Def. (R. Blanchard), Gordius violaceus, Baird (Topsent), and Gordius pustulosus, Baird (Parona).