302 



CCELHELMINTHES. 



Us* half to three quarters of an inch in length, the male and female 

 always in pairs, cause the disease known as 'gapes 'in fowl. Ankylo- 

 stomum (Dochmius) duodenale*(ftg. 266), about two fifths of an inch in 

 length, lives in the small intestine of man, causing severe loss of blood 

 and the disease known as Egyptian chlorosis. The eggs develop in mud 

 and moist earth, and hence people who drink muddy water (Fellahin of 

 Egypt) or work much with clay (potters and brick-makers) are especially 

 subject to infection. It was first known in Egypt, caused considerable 

 trouble during the building of the St. Gotthard tunnel in Switzerland, 

 and now is common in Germany. Recently it has been thought that the 



Ankylostoma larvae obtain entrance to- 

 man through the skin, as in bathing, 

 etc. 



Family 4. TRICHOTRACHELID.E. These 

 owe their common name of ' hair necks ' 

 to the fact that the part of the body 

 which contains the pharynx is hair-like 

 and elongate, while the pharynx itself 

 traverses a peculiar cord of cells. Long- 

 est known of the family is Trichocepl talus 

 dispar* of man (fig. 267), about an inch 

 or an inch and a half in length, which 

 lives with its neck burrowed like a cork- 

 screw in the wall of the intestine near the 

 caecum. Since it does not move, it causes 

 little injury. Its presence can be recog- 

 nized by the oval brown double-shelled 

 eggs (fig. 246, d) in the faeces. 



A second species, Trichina spiralis * 

 (figs. 268, 269), is much smaller, but much 

 more dangerous. Two stages are to be 

 distinguished, the encysted muscle Tri- 

 china and the sexually mature intestinal 

 Trichina. The first was discovered in a 

 human body in 1835; the latter was not 

 known until much later, its history being 

 worked out by Leuckart, Virchow, and 

 Zenker. In the encysted stage it occurs 

 in the muscles of pigs, rats, mice, man, 

 rabbits, guinea pigs, dogs, etc. (never in 



FIG. 267. 



FIG. 269. 



FIG. 268. 



intestinal wall. (From Leuck- birds), enclosed in an oval capsule about 

 FiG. ai 268. Trichina spiralis, male. 0.4 to 0.6 mm. long and hence recogniz- 



tesTe HatSCbek) ' ''*' cloaca: '' able by a practised observer with the 

 FIG. 269. Trichina in muscle. (From naked eye. They are more easily seen 



when they are partially calcified and 



have a whitish color. Certainty in their recognition demands a low power 

 of the microscope. In the capsule is coiled up the worm, about 1 mm. 

 long, which is not yet sexually mature, although furnished with the 



