THE TR1CH.INJE. 



251 



by the muscular fibres or glands. The chitinous tube of the pharynx may have longitudinal 



projections called teeth, but the office of the gullet is that of a sucker or tube. In some ISTematoidea 



the intestinal canal, in part or wholly, undergoes retrogressive development during the parasitism. 



The skin, more or less tough, and often striated across, is formed of several layers partly composed of 



fibres, and rests on a soft, finely 



granular tissue with nuclei. 



Beneath this is a musculo- 



cutaneous envelope with flat 



and fusiform muscular fibres. 



The surface of the skin may be INTESTINAL CANAL OF A NEMATOID. (After Gegenbaw.) 



covered with ridges, tubercles, 



spines, or hair, and moulting takes place in the young. Some Nematoidea have eye-spots, at the 



end of the body, with or without refracting bodies in them. Most have the sexes sepai-ate, and 



usually the males are smaller than the females. 



Of late years much attention has been paid to a very remarkable ISTematoid parasite which has 

 been called Trichina spiralis by Owen. Gritty particles were found in human muscles, by the late 

 Mr. Hilton, F.R.S., of Guy's Hospital, who recognised them as the results of parasites. Sir James 

 Paget, when a student, first determined the existence of the minute worms which produce the 

 gritty parts; and Robert Brown, the botanist, assisted, by lending his microscope to the now 

 distinguished surgeon. In the year following, Professor Owen described the worm scientifically, from 

 .specimens sent him by Mr. Wormald, Paget's colleague. Leuckart discovered the history of the 

 parasite, tracing it to its source and method of propagation ; and Zenker explained the symptoms of 

 infected men, and detected the young in the act of migration. 



The worm was named from its very commonly being seen in a capsule, rolled up in a spiral shape. 

 When mature and able to reproduce its kind, and therefore fully developed, Trichina spiralis is 

 minute, and the male is about T Vth, and the female ^th of an inch in length. The body is 



rounded and filiform, usually slightly bent upon itself, and 

 is i-ather thicker behind than in front. The head is narrow, 

 finely pointed, unarmed, and has a simple central, minute, 

 oral opening. The tail of the male has a bilobed end sur- 

 rounding the vent. The female is stouter than the male, 

 bluntly rounded posteriorly, and the reproductive outlet is 

 placed far forwards. The eggs measure TirW^ 1 f an inch 

 from end to end. As observed in the mxiscles of the human 

 body, the Trichinae are young, not mature, and are spirally 

 coiled worms in the interior of small oval cysts, which are 

 scai'cely visible to the naked eye. They measure y^th of an 

 inch in length, and y-j^th of an inch in breadth, and often 

 are gritty from the presence of salts of lime. Sometimes 

 they are not thus encysted, and they measure -^th f an 

 inch in length, and -g^th of an inch in breadth. The history 

 of the life cycle of the worm is as follows : 



The mature and reprodvictive Trichina inhabits the 

 intestinal canal of Mammalia, including man, and its life 

 lasts from four to five weeks, and they attain their full 

 development and ability to reproduce on the second day of 

 their introduction to their locality. The eggs of the female are 

 hatched, as it were, within her uterus, and produce minute hair-shaped embryos there, and there may 

 be from ten to fifteen thousand of them. The embryos are expelled from the body of the mother 

 whilst in the intestines of the victims, and they soon drill their way through the mucous and muscular 

 tissues of the parts, and then, traversing even serous membranes, get into the muscles. There 

 they assume the form known as Trichina spiralis. The importance of the discovery of this series of 

 -changes is great, for it is clear that if the Trichinae can be kept out of the digestive organs of an 



TRICHINA Sl'IKALIS. 

 u, worm; o, brad ; A, worm coiled up In capsule or cysi In 



