-Doc. 895 



Plate II. 



FIG. 1.— PONDS FOR EXPERIMENT WORK. 



Earth-walled ponds of various sizes and forms present natural conditions sucli as may bo repro- 

 duced on the farm. Small concrete-hned ponds serve the needs of special experiments. Both 

 fish and mussels are reared here. 



FIG. 2.— TROUGHS FOR REARING MUSSELS. 



In troughs supplied with naturally clarified water flowing from near the surface of one rf the 

 ponds, the best conditions have been found for rearing several species of fresh-water mussels. 

 As is the fortune of experimental work, success has been variable, but a single trough may pro- 

 duce in one season more than 2,000 young mussels one-fourth to one-half inch in length. 



