Makch 9, 1900.] 



SCIENCE. 



385 



numbers of other animals, as occasionally 

 one finds in the mud of shallow lakes large 

 numbers of fresh- water hydra. Most if not 

 all 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, how- 

 ever, we find forms which are characteristic 

 of those regions, although they may be 

 mingled with others that are also found in 

 the littoral region. In the abyssal region 

 of Green Lake, which may be considered 

 the typical deep-water lake of Wisconsin, 

 are found, besides some undetermined 

 worms, a little lamellibranch, Pisidiimi, os- 

 tracods, amphipods, insect larvae and Mysis. 

 There are some protozoa in the mud, but 

 they have not been studied. The ostra- 

 cods are so numerous that their shells form 

 a conspicuous part of the bottom deposit. 



In the smaller lakes of a depth ranging 

 from 60 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 con- 

 siderable disappointment because of my 

 interest in .abyssal animals. The probable 

 explanation seems to be that these depths 

 are rendered unfit for life by reason of the 

 more complete stagnation of the deep water 

 in small 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, sink- 

 ing to the bottom, increase largely the 

 amount of decaying organic matter. Partly 

 decomposed leaves are common in the bot- 

 tom 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 bottom 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 cur- 

 rent. 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 

 perfect stagnation, and hence the condi- 

 tions of the bottom are more favorable for 

 animals than in a small lake. The larger 

 the lake, then, other conditions being equal, 

 the greater would be the abundance of abys- 

 sal life. While there have been no accurate 

 means of comparing the abyssal fauna of 

 the Great Lakes with that of the smaller 

 lakes as to quantity, such collections as 

 have been made would indicate that it is 

 much greater in the Great Lakes, and de- 

 creases in proportion to the degree of stag- 

 nation. If my explanation proves to be 

 the correct one, as I feel quite certain it 

 will, it will follow that the small deep lake 

 will be limited in its fauna in two ways : 

 because of its steep shores it will have a 

 small littoral fauna and flora, and because 

 of its stagnant deep water it will have little 

 or no abyssal fauna. 



I have thus far spoken as though all 

 lakes had the three faunae : littoral, limnetic, 

 and abyssal. Generally speaking this is 

 true, even small bodies of water showing 

 this distinction. But occasionally the dis- 

 tinction is almost lost. This is true in 

 Lake Winnebago. In spite of its great 

 size — the lake is some twenty-eight miles 

 long by ten or twelve broad at its greatest 

 width — it is only about twenty-five feet 

 deep. In its fauna there is a curious ming- 

 ling of littoral and limnetic forms, littoral 

 forms being found in the open lake, and 

 limnetic forms even among the weeds along 



