TEICHOTEACHELID^ OR WHIP-WOKMS. 75 



Triohotrachelid^ or Whip-worms. 



The Whip-worms are known by having a long, thin, neck-like 

 anterior portion to the body. A small mouth is present at the 

 tip of this long thin region ; it is not provided, as in many 

 worms, with lip-like papillae. They are all small slender worms, 

 with an anus or (in the male) a cloacal opening at the hind end 

 of the body. There is no bursa, as in the Palisade-worms, and 

 one spioulum alone is present. 



The two most noteworthy genera are TrichocepTialus and 

 TricUnella (fig. 28). 



Trichocephalus is a small worm, with the anterior part of the 

 body much attenuated and whip-like, the posterior part being 

 thick and cylindrical ; this latter contains the generative organs, 

 which are coiled in the male. The eggs are curious citron- 

 shaped, hard-shelled bodies, and undergo their development in 

 water. It is found that the Triohocephalidee require no inter- 

 mediate host, so that they can be taken direct in drinking 

 water or unclean food. 



They do not live free in the gut, but have the whip-like 

 anterior extremity buried in the mucous membrane of the 

 intestine. These worms are found in man, the pig, and the 

 sheep, and cause serious intestinal disturbances. The young 

 worms are hair-like, and resemble very much the trichinae 

 found in pork. 



Another curious form is known as Trichosomum, in which 

 the male is very degenerate and lives in the uterus of the 

 female, as many as three or four males being found in one 

 female. 



This " degeneration " is a very common phenomenon in 

 parasitic life. Any part of an animal that is not used we find 

 degenerates, and may become lost entirely unless nature utilises 

 it for some other purpose. The second pair of wings in the 

 true flies {Dipterrd) have apparently degenerated, but they are 



