180 Wisco7isin Academy of Sciences, Avis, and Letters. 



not all of these animals are identical with the littoral forms, and 

 the difference between the littoral fauna and the deep-water 

 fauna is that in the deep water those forms which are especially 

 dependent upon the weeds for food and protection are lacking, 

 while we find in abundance the mud dwellers. 



In the abyssal regions of deep lakes, however, we find forms 

 which are characteristic of those regions, although they may be 

 mingled y^'ith others that are also found in the littoral region. 

 In the abyssal recrion of Green Lake, which may be considered 

 the typical deep-water lake of Wisconsin, are found, besides 

 some undetermined worms, a little lamellibranch, Pisidium, os- 

 tracods, amphipods, insect laryie and Mysis. There are some 

 protozoa in the mud, but they have not been studied. The os- 

 tracods are so numerous that their shells form a conspicuous part 

 of the bottom deposit. 



In the smaller lakes of a depth ranging from GO to 100 feet, 

 like the Waupaca lakes and Elkhart, a different condition of 

 things exists. The bottom is composed of a dark mud, and is 

 almost completely devoid of life. This has been a puzzling fact, 

 and has been to me personally a matter of considerable disap- 

 pointment because of my interest in abyssal animals. The prob- 

 able explanation seems to be that these depths are rendered unfit 

 for life by reason of the more complete stagnation of the deep 

 water in sm^all lakes, and because of the larger amount of 

 organic matter which is being decomposed there. Because of 

 the small areas of such lakes, leaves are carried from the shore 

 all over their surfaces, and, sinking to the bottom, increase 

 largely the amount of decaying organic matter. Partly decom- 

 posed leaves are common in the bottom collections of small lakes 

 but rare in lakes of the size of Green Lake or Lake Geneva. This 

 may account largely for the black color of the bottom mud. 

 Then, in a large lake, the winds indirectly produce slow bot- 

 tom currents. A prevailing wind will pile up the water at the 

 end of a lake ; this water must return in some way, and there 

 is good reason to think that at least a part of it returns by a slow 

 bottom current. Professor Birge tells me that his temperature 

 observations give evidence of such a movement of the water. It 

 follows, probably that in the large lake there is not nerfect stag- 



