CONTENTS. 



Page. 



Introduction 79 



Part I . Natural history of fresh-water mussels 81 



Habits 81 



Conditions of existence 81 



Locomotion 82 



Density of population 84 



Breeding 85 



Winter habits 85 



Feeding habits 86 



Food of mussels 87 



Significance of the problem 87 



Observations of Franz Schrader on food of mussels 88 



Species studied 88 



Food content of waters 88 



Food discrimination under normal conditions 89 



Utilization of food materials 89 



Experiments in feeding vegetable matter 89 



Experiments in feeding animal matter 90 



General obser^'ations 90 



Obser\-ations of H. Walton Clark on food of mussels 91 



Observations of A. F. Shira on food of juvenile mussels 93 



Habitat 94 



Body of water 94 



Streams 94 



Lakes 97 



Ponds, sloughs, marshes, and swamps 100 



Artificial ponds and canals 100 



Bottom loi 



Depth 107 



Light no 



Current in 



Water content 113 



Suspended matter 114 



Minerals in solution 114 



Dissolved gases iij 



Vegetation 118 



Animal associates 119 



Parasites and enemies 121 



Parasites 121 



Enemies 122 



Conditions unfavorable for mussels 123 



Natural conditions 123 



Artificial conditions 124 



Growth and formation of shell 125 



Measurements of giowth 125 



Presence of so-called growth rings ■. 129 



Mode of formation of shell 129 



Significance of rings 132 



Abnormalities in growth of shell 133 



75412°— 22 6 77 



