174 American Fisheries Society 



you, ivithout the mud. A weir and gate which can be 

 tightly closed is located at the central point in the neck 

 of the dumb-bell; consequently, the two ponds can be 

 operated together or modified independently, since the 

 water supply is absolutely independent. We can operate 

 one side with rain water and the other with city water. 

 We can modify water conditions of one without affecting 

 in the least those in the other ; or if desired, the two may 

 be joined by an open connection such as to insure rela- 

 tive, if not absolute, uniformity in the two parts. 



In one of these plants has been incorporated a sugges- 

 tion that we owe to the kindness of Superintendent 

 Dwight Lydell, of Michigan. In one of the two ponds 

 has been constructed a series of small islands. The area 

 and location of these have been planned so exactly that the 

 shoreline of the east pond is just twice as great as the 

 shoreline of the west pond, but the water area and the 

 water volume are substantially identical. A small bridge 

 thrown over the neck that joins the two ponds gives en- 

 trance to the experimental laboratory building. The 

 whole tract of land, including buildings and ponds, is to 

 be surrounded by a cat and boy proof fence, far enough 

 from the outer edge that no combination of bamboo pole 

 and bent pin can possibly prove successful in robbing 

 the experimental ponds of their treasures. 



Each pond has a kettle with a maximum depth of 12 

 to 13 feet. The outlet from the kettle is surrounded by a 

 box from which a plank bridge extends to the shoreline. 

 An inlet is located in the communicating neck, and one 

 inflow point is located on each side of the gate separating 

 the two ponds. In this installation attention has been 

 paid to the fact that in this region it is not possible to use 

 water, lavishly. It is in one sense the dryest point in the 

 state of Illinois, for it lies on the height of land between 

 Chicago and the Gulf. Several of the rivers of this re- 

 gion originate as tiny streams, within a few miles, or less, 

 of the very point where this plant is located. There are 

 now in the county no lakes and very few permanent 

 streams of any size. Extensive drainage ditches have 

 eliminated surface moisture, but even before their con- 



