TYPE NEMATIIELMINTHES. 



177 



tissue and finally reach the muscles, especially of the neck and diaphragm, 

 into which they bore, producing a degeneration of the tissue upon which 

 they feed. In the course of the third month after infection they encyst 

 themselves in the muscle-tissue, and inflammatory changes produced in the 

 connective tissue in their immediate vicinity result in the formation of a 

 second cyst-wall around them (Fig. 88, A). If the intestinal inflammation 

 and the succeeding muscular inflammation have not proved fatal to the 

 host, the danger is past, the encapsuled Trichince undergoing no further 

 development in the muscles. 



Other forms which occur in man are Ascaris lumbricoides, the round- 

 worm (Fig. 88, B), a large form, of which the female measures 40 cm. in 

 length and the male 25 cm., and which bears some resemblance in shape to 

 an earth-worm, Oxyurisvermicularis, asmaller form, 1 cm. in length, which 

 inhabits the rectum especially of young children, and Trichocephalus dispar 

 (Fig. 88), which measures 3-5 cm. in length and is characterized by the 

 anterior half of the body being exceedingly slender, the worm boring into 

 the intestinal wall, especially in the neighborhood of the cajcum, by this 

 slender portion, the hinder thicker por- 

 tion hanging freely in the wall of the 

 intestine. The presence of these three 

 forms may be recognized, independently 

 of the finding of the actual worm, by 

 their ova, whose respective characters dif- 

 fer very greatly. So far as is known the 

 development of these forms is direct and 

 there is no intermediate host, but the ova 

 are taken into the body with the food. 

 The exact manner of infection is, how r ever, 

 obscure. 



In addition to the forms which have 

 been mentioned there are a few which are 

 more especially frequent in tropical cli- 

 mates. Dochmius duodenalis is a small FIG. 88. A, TrichintT^ucysted 



form about 1-2 cm. in length, with strong in muscle; B, anterior extrem- 

 teeth or blunt spines in the mouth region, 

 which fastens itself to the wall of the 

 small intestine and lives upon the blood 

 of its host, producing auasmia. Its ova 

 develop in stagnant water or damp earth, 

 and probably man becomes directly in- 

 fected. It has long been known in the tropics, producing the disease 

 known as Chlorosis (egyptiaca, but may also affect miners or workers in 

 tunnels, having appeared endemically in the workers on the St. Gothard 

 tunnel, whence it has since spread somewhat in Germany, especially among 

 workers in clay. Filaria medinensis is limited entirely to the tropics and 

 is a very slender worm nearly 1 metre in length which lives in the connec- 



ity of Ascaris lumbricoides 

 from theveiitral surface, show- 

 ing the two ventral oral papillae 

 and the excretory pore (both 

 after LEUCKART) ; C, Trichocepk- 

 alus dispar (after OWEN). 



