BAKER: FIELDBOOK OF ILLINOIS LAND SNAILS 25 



One relationship between snails and other animals is com- 

 monly overlooked. In the bodies of many kinds of snails para- 

 sitic worms undergo a necessary part of their development. 

 Fortunately, none of the Illinois land snails is known to harbor 

 parasitic worms directly of importance to man. There are, 

 however, many species of land snails whose bodies shelter 

 parasites belonging to the flatworm group known as the flukes or 

 Trematoda. These worms, growing inside the bodies of land 

 snails, never reach maturity in the snails, which are called in- 

 termediate hosts. For full development the trematode must 

 enter the body of some mammal, bird, amphibian or reptile. 

 Relatively little is known of the life-history details of these 

 parasitic worms carried by land snails in Illinois, though the 

 larvae have been frequently observed. 



Collectors of Illinois Land Snails 



Many eminent students of science have contributed to our 

 knowledge of the nature and extent of the land snail fauna of 

 Illinois. Chief among these is Thomas Say, father of American 

 conchology, who lived for a time at New Harmony, Indiana, 

 and who studied and gave names to many species common in 

 our state. Amos Binney and his son, William G. Binney, were 

 the first to place the fauna on a scientific basis of classification, 

 and not a few of our species have the names of these famous 

 conchologists as their describers. The name of Thomas Bland, an 

 intimate associate of William G. Binney, is indelibly connected 

 with the study of land snails of Illinois and other part? of North 

 America. Augustus A. Gould of Boston, Isaac Lea of Philadelphia 

 and Bryant Walker of Detroit have contributed largely to the 

 subject. Among living students of this branch of science who 

 have studied the Illinois fauna is Henry A. Pilsbry of Philadel- 

 phia, who has placed the subject on a sound basis of classification 

 and whose treatment has been followed in this fieldbook. H. B. 

 Baker of Philadelphia and George H. Clapp of Pittsburgh, dis- 

 tinguished students of the land snails, have added much to our 

 knowledge of some of the species of land snails that live in Illi- 

 nois. 



Many citizens of Illinois have studied and collected the 

 land mollusks of the state and have left a large and interesting 

 bibliography. Most of these are now dead, and few others have 

 become interested enough to take their places. 



