WORMS. 197 



nant waters, through which roads pass, they fasten on 

 the feet of barefoot travelers and suck their blood. 



The Dentdlium (dentalium entale). plate 25, fig. 7, 

 is a worm that lives in a single shell, which bears a min- 

 iature resemblance to an elephant's tusk. It buries itself 

 perpendicularly in the sand with the pointed end down- 

 wards, scarcely as thick as a quill, smooth and slightly 

 red. Its length exceeds an inch. Found in all the seas 

 in Europe. 



SECOND ORDER. 

 INTESTINAL WORMS. 



These are a numerous spscies, and inhabit the intes- 

 tines of many animals, causing pain, disease, and often 

 death. The most common are 



The Ascarides (ascaris lumbricoides), which resemble 

 the rain worms in the cylindrical form of their bodies ; 

 they are as thick as a quill, sometimes a foot long, and 

 have the mouth furnished with three fleshy tubercles. 

 They are common to almost every one in childhood, but 

 in later life, except in some few cases, disappear. San- 

 tonin is considered a specific. 



The Guinea Worm (vena medinensis) is sometimes 

 five or six feet long, and about as thick as the largest 

 string of a violin. Very common in hot climates, where 

 it insinuates itself under the skin, generally of the leg, 

 where it causes excruciating pain and severe cramps. 

 When this is the case the skin must be opened, and the 

 worm extracted very slowly for fear of breaking it. The 



