542 



ber, twelve hauls of the dredge and three of the trawl, aggregating about 

 three miles in length, so distributed in distance and depth as to give a 

 good idea of the invertebrate life of the lake at that season. 



And now if you will kindly let this suffice for the background or 

 setting of the picture of lacustrine life which I have undertaken to give 

 you, I will next endeavor — not to paint in the picture ; for that I have 

 not the artistic skill. I will confine myself to the humble and safer task 

 of supplying you the pigments, leaving it to your own constructive im- 

 aginations to put them on the canvas. , 



When one sees acres of the shallower water black with water-fowl, 

 and so clogged with weeds that a boat can scarcely be pushed through the 

 mass ; when, lifting a handful of the latter, he finds them covered with 

 shells and ahve with small crustaceans ; and then, dragging a towing 

 net for a few minutes, finds it lined with myriads of diatoms and other 

 microscopic algae, and with multitudes of Entomostraca, he is likely to 

 infer that these waters are everywhere swarming with life, from top 

 to bottom and from shore to shore. If, however, he will haul a dredge 

 for an hour or so in the deepest water he can find, he will invariably 

 discover an area singularly barren of both plant and animal life, yielding 

 scarcely anything but a small bivalve moUusk, a few low worms, and red 

 larvae of gnats. These inhabit a black, deep, and almost impalpable 

 mud or ooze, too soft and unstable to afford foothold to plants even if 

 the lake is shallow enough to admit a sufficient quantity of light to its 

 bottom to support vegetation. It is doubtless to this character of the 

 bottom that the barrenness of the interior parts of these lakes is due; 

 and this again is caused by the selective influence of gravity upon the 

 mud and detritus washed down by rains. The heaviest and coarsest of 

 this material necessarily settles nearest the margin, and only the finest 

 silt reaches the remotest parts of the lakes, which, filling most slowly, 

 remain, of course, the deepest. This ooze consists very largely, also, of 

 a fine organic debris. The superficial part of it contains scarcely any 

 sand, but has a greasy feel and rubs away, almost to nothing, between 

 the fingers. The largest lakes are not therefore, as a rule, by any means 

 the most prolific of life, but this shades inward rapidly from the shore, 

 and becomes at no great distance almost as simple and scanty as that 

 of a desert. 



Among the weeds and lily-pads upon the shallows and around the 

 margin — the Potamogeton, Myriophyllum, Ceratophyllum, Anacharis, 

 and Chara, and the common Nelumbium, — among these the fishes chiefly 

 swim or lurk, by far the commonest being the barbaric bream^ or "pump- 

 kin-seed" of northern Illinois, splendid with its green and scarlet and 

 purple and orange. Little less abundant is the common perch (Perca 

 lutca) in the larger lakes — in the largest out-numbering the bream itself. 

 The whole sunfish family, to which the latter belongs, is in fact the 

 dominant group in these lakes. Of the one hundred and thirty-two fishes 

 of Illinois only thirty-seven are found in these waters — ^about twenty- 



•Lepomis gibbosus. 



