«IAM lf{ 1900 



Article YIII. — .1 St(tfi.'itic<tl Sii((lij of the I'dni.sites of the 

 Vnhmhhr. By H. M. Kelly. 



The studies on the quantitative occurrence of parasites in 

 different species of the Uriion'Khp which form the basis of the 

 present paper were made at the Illinois Biological Station, at 

 Havana, early in the summers of 1896 and 1897 and con- 

 tinued both seasons at Mt. Yernon, la., and at Lewisburg and 

 Phoenixville, Pa., the material used being secured in the 

 above mentioned localities and examined while fresh. It 

 was the purpose of the investigation to determine, if possible, 

 under what conditions infestation would be found to vary in 

 a series of closely related species of a given locality or of 

 several localities, and to what extent this variation could be 

 regarded as a specific characteristic. 



The Illinois, Iowa, and Pennsylvania waters from which 

 collections were made are indicated in Table I., and for the 

 purposes of this paper may be brietiy characterized as fol- 

 lows : (1) The Illinois River at Havana is a large sluggish 

 stream with alluvial banks and largely muddy bottom, full 

 of organic matter of various origin. (2) Spoon Paver, a 

 tributary of the Illinois, is at Bernadotte and Duncan's 

 Mills, where collections were made, small, with rapid current 

 and rocky bottom. It drains a purely agricultural region, 

 and is subject to frequent and sudden floods. (3) Quiver 

 Creek, near Havana, is a smaller tributary to the Illinois, 

 draining a sandy plain. (4) Thompson's Lake is a shallow 

 body of water about six miles long and one mile wide, lying- 

 in the low alluvial flood plain of the Illinois Eiver, with very 

 muddy bottom and little change of water except as affected 

 by change of level in the river, with which it is connected. 

 (5) The Cedar Piver, near Mt. Yernon, la., is a rapid shallow 

 stream with shifting sandy l»<>tt(»m for the most part, draining 



