NEMATODA. 



355 



projected. Tr. spiralis Owen, in the alimentary canal of Man and numerous, 

 principally carnivorous, Mammalia ; hardly two lines in length. The viviparous 

 females begin to bring forth embryos about eight days after their migration 

 into the alimentary canal. These embryos traverse the intestinal walls and 

 body cavity of the host, and migrate, partly by their own movements in the 

 bundles of connective tissue, partly with the aid of the currents of blood into 

 the striped muscles of the body. They pierce the sarcolemma and penetrate 

 into the primitive bundles, the substance of which degenerates, the degeneration 

 being accompanied by an active 

 multiplication of the nuclei. In 

 a space of fourteen days they 

 develop, within a sac-like swelling 

 of the muscle fibres, into spirally 

 coiled worms, around which and 

 within the sarcolemma and its 

 connective tissue investment a 

 clear lemon -shaped capsule is 

 excreted from the degenerated 

 muscle substance. The young 

 Muscle- Trichina can remain liv- 

 ing for years within this capsule, 

 which at first very delicate, gra- 

 dually becomes thickened and 

 hard by the formation of other 

 layers and by the gradual deposi- 

 tion of calcareous matter. If the 

 encysted animal is transferred 

 into the intestine of some warm- 

 blooded animal in the flesh of its 

 first host, it is freed from its cyst 

 by the action of the gastric juice, 

 and the rudimentary generative 

 organs, which are already toler- 

 ably far developed, quickly attain 

 maturity. In from three to four 

 days after their introduction the 

 asexual Muscle-Trichinas become 

 sexual Trichinas. These copulate 

 and produce a brood of embryos 

 which migrate into the tissues of 

 the host (one female may produce FIG. 287. Filarla medinenl* (alter Bastian and 

 as many as 1000 embryos) (fig. ^uckart). a.Anterior end seen from the oral sur- 

 ,. . J . face; O, mouth; P, papilla, b, Pregnant female 

 286). The house rat is especially (siZ3 reduced more tnan half) . c> Embryo8 



to be mentioned as the natural strongly magnified, 

 host of the Trichina. This 



animal does not hesitate to eat the carcase of its own species, and so the 

 Trichina infection is passed on from generation to generation. Carcases in- 

 fected with Trichinas are sometimes eaten by the omnivorous pig, in whose 

 flesh the encysted Trichinas are introduced into the intestine of man, and 

 occasion the well-known disease, Trichinosis, which when the migration takes 

 place in number, often has a fatal result. 

 Fam. Filariidae. Body filiform, elongated, often with six oral papillae, some- 



