The genus Eustrongylus includes two species, E. gigas Rud. and E. tubifex Nitsch. The former attains in the female the gigantic length of 860 mm., with a breadth of 7 mm. and a weight of over 40 grs.[[181]] The male is a quarter to a third as long as the female. This parasite inhabits the kidney capsules of carnivorous animals, especially of those that eat fish, such as dogs, seals, etc., and has occasionally been found in man, the horse, and the deer. It frequently destroys the substance of the kidney. The worms are red in colour. The eggs die when exposed to desiccation for a few days, but have been kept alive for fifteen months in water; it is believed by Schneider and Leuckart that they are eaten by fish, and that the larvae form the Filaria cystica found in the peritoneal membrane of the fishes Galaxias scriba and Symbranchus laticaudatus, and that they pass into their final host, where they become sexually mature, by the latter eating raw fish. E. tubifex is found in aquatic birds, e.g. ducks, grebes, and divers, etc.
The genus Strongylus is easily recognised by its conspicuous genital bursa, strengthened by variously arranged ridges which are of specific value. There are numerous species, found in man and many other mammals, and also in birds and reptiles. Some species inhabit the intestine, others form aneurisms in the large blood-vessels, and cause considerable mortality amongst horses; others live in the tracheae and lungs of cattle and sheep, their presence often causing great loss to the farmer. No intermediate host has been satisfactorily demonstrated; the larvae live in damp earth, and it seems almost certain that they pass directly into their host with its food.
Dochmius (Ancylostomum) duodenalis, called by Neumann[[182]] Uncinaria duodenalis, is one of the most dangerous parasites that attack man. It lives in the duodenum and jejunum, and the fertilised eggs leave the body of its host with the excreta, and in damp earth develop into larvae in the course of a few days. These at first eat voraciously, but after undergoing several moults they cease to take food and pass into the resting stage. If now they are swallowed with drinking water, they come to rest in the small intestine of their host, and in a few weeks become sexually mature. They cause great harm by burrowing in the intestinal walls and destroying the capillaries. They are found by hundreds, and even thousands, in the same host, and produce profound anaemia, which is frequently fatal to miners, and was the cause of a great mortality amongst the workers in the St. Gothard Tunnel some fifteen years ago. This species is very widely spread over the face of the globe. Dochmius trigonocephala Rud. and D. stenocephala produce similar diseases in dogs and cats, and D. cernua Crep. is found in sheep and goats.
The genus Cucullanus exists in the adult form in the intestines of fishes, and more rarely of reptiles. C. elegans Zed., which live in fresh-water fish, e.g. the perch, is viviparous; after birth the young pass into the water and make their way into the alimentary canal of the small crustacean Cyclops, and thence into its body-cavity. Here they undergo two moults, accompanied by certain changes in structure. If this second host be swallowed by a fish the parasites are set free, and develop generative organs. Ollulanus tricuspis Leuck., which in the adult state is found in the cat, chiefly in the intestine but also in the bronchi and other parts, gives rise to larvae which are of enormous size compared with the parent; these leave the body, and if eaten by a mouse encyst in its muscles, and if the mouse be devoured by a cat, they complete their life-cycle by becoming sexually mature.
The genus Syngamus infests the trachea and bronchi of birds, more rarely of mammals. The red- or forked-worm, Syngamus trachealis Sieb., is common in poultry and game birds, and causes the disease known as gapes, which is especially common in young birds, and often gives rise to extensive loss. The peculiarity of this genus is that the male is permanently attached to the female, its genital bursa being so closely adherent to the opening of the oviduct that two specimens cannot be separated without tearing the tissues. The ova are not laid, but escape from the body with fully-formed embryos in them, by the decay or rupture of their parent's body. They hatch in damp earth or water in from one to six weeks according to the temperature. When swallowed by a fowl they develop into adults, which reproduce eggs in less than three weeks. No second host is needed, but the embryos remain alive in the alimentary canal of earthworms, and these doubtless to some extent serve to spread the disease.
Fig. 70.—Syngamus trachealis Sieb., natural size and magnified four diameters. The small ♂ is permanently attached to the female. (From Warburton.[[183]])
III. Family Trichotrachelidae.
This family is characterised by the anterior end of the body being produced into a long whip-like neck. The mouth is small and devoid of papillae. The oesophagus is very long, and it traverses a peculiar strand of cells.
Genera: Trichocephalus, Trichina, Trichosoma, and others.