Article XII. — The Hirudinea of Illinois. By J. Percy 

 Moore. 



This paper is a partial descriptive catalogue of the leech 

 fauna of Illinois. It is founded on collections gathered from 

 time to time during the past twenty-five years by the Illinois 

 State Laboratory under the direction of Prof. S. A. Forbes, of 

 which material by far the most important part, as regards 

 both number of species and individuals and state of preser- 

 vation, is that taken by Prof. Frank Smith and other mem- 

 bers of the staff of the Illinois Biological Station. For the 

 opportunity of studying this material I am indebted to the 

 interest and courtesy of Professors Forbes and Smith. No 

 doubt other species occur in this region ; indeed several 

 others have already been recorded from the State. 



No general morphological questions are discussed herein, 

 though the specific descriptions include some evidence point- 

 ing to several generalizations of fact and theory which will 

 be evident to the reader. The nomenclature of somites and 

 annuli used, is that suggested in two recent papers (Moore 

 '98 and 1900). Some differences (in the enumeration of 

 somites of certain species) between this paper and the earlier 

 one just mentioned are due to the recognition of an additional 

 somite in the preocular lobe, as pointed out by Apathy ('88) 

 and Whitman ('92), and the adoption of the neuromeric 

 standard for the determination of somite limits as maintained 

 by Castle (1900) and Moore (1900). A sharp distinction has 

 not always been made between the different kinds of cutaneous 

 sense organs, unless such distinctions are readily discernible 

 in surface views. Eyes are described as single if they appear 

 so in surface views, even though sections show them to be 

 compound. In the figures the pigment cups alone of the eyes 

 are exhibited, so that in some cases they are indicated in 

 somites different from those which furnish their sensory 

 cells. In fact, with very few exceptions, the descriptions 

 have purposely been restricted to such features as are 



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