12 ILUNOIS BIOLOGICAL MONOGRAPHS [206 



BIOLOGY 



TYPES OF LOCALITIES 



During the past three years collections have been made in some eighty 

 streams and ponds. The territory thus covered comprises several regions: 

 in Illinois, the vicinity of Urbana and Havana in the central part, and at 

 Cedar Lake in the north; in Iowa, regions near Fairport and Grandview along 

 the Mississippi river and near Grinnell in the central part of the state; in Minne- 

 sota, at Homer which is in the south eastern corner ; in Wisconsin, at Milwaukee. 

 About fifty places have been visited only once, a number of others two or three 

 times, while from a few, collections were made every few days for several 

 months. The immediate surroundings, the state of the weather, the condition 

 of the water, all varied to a greater or less degree. There were gradations from 

 a sandy barren flat to a wooded hillside, from a hot July day to the intense cold 

 of mid-winter with ice five feet in thickness, from a few quarts of thick muddy 

 water to a stream the size of the Mississippi. The types of places investigated 

 may be summarized as streams, ponds, springs, and temporary mudholes. 



Springs and puddles seem to be unfavorable for many of the smaller animal 

 forms, except in a few instances. In one place where the location made it 

 possible and where the spring furnished sufficient water to make a fairly per- 

 manent little pond, both the plant and animal forms had a chance to develop 

 and were present in abundance. Here Stenostoma was found in great numbers. 



If puddles are made by the overflow from some stream or larger pond, 

 then the plant and animal forms present will be those of the main supply which 

 have become marooned. They will eke out an existence as long as conditions 

 permit, or will thrive if chance favors them. Thus in some years the rains are 

 not so heavy as to stir up a pond violently, and then if the situation is partly 

 protected from the drying power of the sun the imprisoned fauna and flora 

 may flourish thruout the season. If the water remains for some length of time 

 so that filamentous algae have a chance to develop, there will probably be also 

 many small crustaceans and an abundance of other fife but no rhabdocoels. 

 That is, species capable of finding transportation thru the air may gain a foot- 

 hold in ponds where other species unable to do this will not. This, perhaps, 

 explains first the presence of certain rhabdocoels in some mudholdes and not 

 in others of different origin yet alike in general condition, and second their pres- 

 ence at one time and not at another. 



The running water of streams and rivers does not produce situations favor- 

 able to delicate free-swimming organisms. Thus the type of turbellarian found 

 in such places will be one able to find a sheltered and protected spot where 

 there is also food and oxygen. At Milan, Illinois, where the Rock river flows 

 over six or eight miles of rocky bed, planarians have an ideal location. Num- 

 bers of specimens are found clinging to the under side of nearly all the stones 



