PARASITES OP ANIMALS. Ill 



biting and snarling at its companions, but is usually too weak 

 to defend himself, if attacked in return, and is easily thrown 

 down. Finally the weakness increases until the poor crea- 

 ture is unable to walk about, or to stand. This parasite will 

 probably yield to the same remedies used for tape-worms, or 

 those employed against the common round-worms of man (yls- 

 caris lumbricoides) , to which, therefore, the reader should refer. 



NEMATODES. 



(^Round-ioorms and Thread-tvorms.^ 

 The Flesh-ivorm (^Trichina spiralis Owen). Figure 76. 

 This most important and most dangerous of all human para- 

 sites, is a very minute round worm, which in the larval state 

 lives in the muscles of man, swine, dogs, cats, rats, mice, 

 rabbits. Guinea-pigs, and many other animals, and in the ma- 

 ture state inhabits the intestines of the same animals. The 

 body is slender, smooth, and round. The intestine is com- 

 posed of a series of small, bead-like swellings, separated by 

 constrictions. The male is much smaller than the female, 

 when mature measuring only xV of ^ii inch ; its body is filiform, 

 pointed at the head, enlarged at the opposite end, generally 

 somewhat bent or curved upon itself ; the head is very small 

 and pointed, unarmed, but with a minute central mouth ; the 

 posterior end of the l)ody is furnished with a bilobed ap- 

 pendage, the anal opening being between the lobes ; the penis 

 is a single spiculum, cleft above so as to have a V-shaped out- 

 line. The female is stouter than the male and longer, meas- 

 uring about |- of an inch, when mature ; the posterior end is 

 bluntly rounded; the genital orifice is at about a fifth of the 

 length from tlie anterior end of the body. They are viviparous 

 and the uterus occupies most of the body, in the form of along 

 and wide tube, in which the embryos are closely packed. The 

 eggs are y^Vo of ^ii mch long. The young Trichina3,like young 

 tape-worms, occur imbedded in the muscles of the hog and 

 various other animals, and man. But unlike the young tape- 

 worms or " measles," the young TricTiince are so small as to be 

 quite invisible to the eye, and millions of them may ex- 

 ist in the flesh of a pig without producing any unusual appear- 

 ance in the meat sufficient to attract the attention even of an 



