114 Aquatic Organisms 



River to be 36,558,462 per cubic meter of water, and he 

 considered them as one of the principal sources of food 

 supply of Entomostraca and other microscopic aquatic 

 animals. St ephano discus (/) is distinguished by the 

 long, hyaline filaments that radiate from the ends of the 

 box, and that serve to keep it in the water. A species 

 of Stephanodiscus having shorter and more numerous 

 filaments is common in the open waters of Cayuga Lake 

 in spring. 



The cells of Meridion are wedge-shaped, and grouped 

 together side by side, they form a flat spiral ribbon of 

 very variable length, sometimes in one or more com- 

 plete turns, but oftener broken into small segments. 

 This form abounds in the brook beds about Ithaca, 

 covering them every winter with an amber-tinted or 

 brownish ooze, often of considerable thickness. It 

 appears to thrive best when the temperature of the 

 water is near 0° C. Its richest growth is apparent after 

 the ice leaves the brooks in the spring. As a source of 

 winter food for the lesser brook-dwelhng animals, it is 

 doubtless of great importance. A view of a magni- 

 fied bit of the ooze is shown in figure 36. 



The colonies of AsterioneUa {n) whose cells, adhering 

 at a single point, radiate like the spokes of a wheel, are 

 common in the open waters of all our lakes and large 

 streams. It is a common associate of Cyclotella, and of 

 Tabellaria and other band-forming species, and is often 

 more abundant than any of these. The open waters of 

 Lake Michigan and of Cayuga Lake are often yellowish 

 tinted because of its abundance in them. Late spring 

 and fall (especially the former) after the thermal over- 

 turn and complete circulation of the water are the 

 seasons of its maximum development. AsterioneUa 

 abounds in water reservoirs, where, at its maxima, it 

 sometimes causes trouble by imparting to the water an 

 aromatic or even a decidedly ''fishy" odor and an 

 unpleasant taste. 



