312 STRONGYLUS ; FILARIA. ACANTHOCEPHAL A. 



the body, but these are rarely found in man. Of this nature is 

 the Strongylus gigas, which inhabits the kidneys of pigs, and 

 sometimes occurs in the human subject. This worm is usually 

 about ten inches in length, but occasionally measures two or three 

 feet, and, as might be expected, is extremely injurious to the 

 animal in which it takes up its abode. We may also notice the 

 Filaria or Guinea-worm, which burrows in the flesh of man 

 and other animals in warm climates, especially in Africa and 

 the South of Asia. It usually measures five or six feet in length, 

 but is said sometimes to be much longer. When it shows itself 

 at the surface, it is extracted very slowly and carefully, by wind- 

 ing it round upon some small object ; if broken during this 

 operation, it is said to produce very painful consequences. The 

 mode of development and transmission of the Nematoid worms is 

 still involved in much obscurity. In some instances the worms ap- 

 pear to bore through the wall of the intestine, in order to deposit 

 their eggs in the tissues or blood-vessels of their host ; the young 

 animals then enclosing themselves in a minute cyst, from which 

 they escape after a time in order to return to the intestine. 

 This is supposed to be the origin of the Trichina spiralis, a 

 small encysted worm found on the muscles of the human subject. 

 In other cases the worms are passed with the excrements, espe- 

 cially at certain seasons of the year, when they probably disse- 

 minate their eggs in the outer world ; and these, or the young 

 brood, may be taken again into the stomach with raw food or 

 water. The little Oxyuris is even known to creep voluntarily 

 out of the intestine, and may thus perhaps find admission to that 

 of a new victim. The Filaria is found principally in the lower 

 extremities of the body, so that its young probably inhabit the 

 water, and attach themselves to the legs of people when wading 

 or washing their feet. The third Order, the ACANTHOCEPHALA, 

 includes only the single genus Echinorhynchus, composed of 

 rather thick, annulated worms, which appear to be totally desti- 

 tute of an intestine. These curious parasites, which are found 

 principally in the intestines of Fishes, are furnished with a pro- 

 trusible proboscis, armed with rows of recurved spines, which 

 serve to hold the animal firmly in the intestine of its host. Be- 



