GENERAL INTRODUCTION 



The leeches, also cald blood suckers by people in general 

 and Hirudinea by the scientist, are distributed all over the world. 

 They are mentioned in the writings of many of the ancients. 

 Herodotus, who was born about 480 B. C. wrote about the leech 

 under the name "bdella", which still forms the ending of some of 

 our scientific names of certain leeches and groups of leeches. Galen, 

 a Greek physician and author born about 130 A. D., recommended 

 the use of the leech for bloodletting. Other Greek and Roman, 

 German, French and English writers wrote about the leech and its 

 habit of sucking blood, so that in a general way leeches became 

 quite well known centuries ago. The medicinal leech in particular 

 became well known thru a great many more or less extended writ- 

 ings on its anatomy and habits and was brought into almost uni- 

 versal use by physicians. It was continued in quite general use 

 until about the middle of the 19th century. Altho this leech in 

 particular was in such general use and it and others frequently 

 became objects of scientific study, we did not get a correct concep- 

 tion of some of the most prominent features of leech structure 

 until 1900. There is still much to be cleared up concerning the 

 structure and life history of many of our leeches. 



Habits. 



Most of the leeches live in fresh water, under stones, leaves 

 and wood, on water plants, in the mud and ooze on the bottom of 

 ponds, lakes and streams, and attacht to other animals. A few 

 live in salt water, a few in moist earth, and a few on land in the 

 forests of tropical and semi-tropical countries. They can crawl 

 about after the manner of the "measuring worms", using their 

 suckers when thus moving about. Those living in the water are 

 also good swimmers. They swim by graceful undulations of the 

 body. Land leeches when dropt into the water usually sink to the 

 bottom and then crawl out. 



Many of the leeches feed on the blood of vertebrates. Some 

 of the bloodsucking leeches remain attacht to their hosts only long 

 enough to become gorgd with blood, and some apparently spend 



