524 



the more delicate of the Protozoa were killed by the pounding of 

 the falling water. Univalve mollusks were not only living, but were 

 breeding here August 25 ; whirligig beetles — mostly Gyrinus analis — 

 were common; large isopod crustaceans — Asellus — were taken here 

 for the first time; and a; few slime worms (Tubifex) were found 

 where soft mud was deposited in sheltered places, the current being 

 too swift for any considerable accumulation of bottom sediments. 



In respect to organisms of other classes, the differences above 

 and below the dam were merely trivial, unless we may attach some 

 importance to the fact that our first specimens of the bryozoan 

 Plumatclla repcns, were taken below. This species was not found 

 above Marseilles, but occurred regularly at the various stations from 

 that point downward. 



Ottawa 



No collections were made at Ottawa in 191 1; and the several 

 oxygen determinations of September 2 of that year are of little use 

 for comparison, since the samples were all taken near the south 

 shore above the mouth of the Fox River, from only six inches be- 

 low the surface, in water but two feet deep. They averaged 5.34 

 parts per million, or 63.1 per cent, of saturation. The carbon diox- 

 ide on this date varied from 4.2 to 5.5 parts per million, with an 

 average of 4.66. 



August 22, 191 2, oxygen tests from each side of the river above 

 the Fox, averaged 3.65 parts per million. November 2 the water 

 of the Illinois above the Fox gave 5.7 parts per million; and that 

 of the Fox itself nearly twice as much (11.2 parts per million). 



In 19 1 2, biological collections were made here for seven days, 

 August 22 to 28 inclusive. Dip-nets, small seines, dredges, the mus- 

 sel-bar, and dynamite, were variously used, according to the situation 

 and the object in view. The water at this time had a distinct sew- 

 age odor, somewhat less noticeable, however, than at Marseilles, and 

 among the weeds along the banks was an oily, tar-like scum similar 

 to what had been noticed in the sanitary canal at Lockport. It ap- 

 parently originated in gas-house wastes. Other more or less recog- 

 nizable objects from the sewage were more abundant here along 

 shore than usual, possibly because a heavy rain which had fallen three 

 days before, bringing the river up about a foot, had flushed out 

 the Des Plaines. 



The river sludge obtained at various points did not differ appre- 

 ciably from that above, either in sensible character or in organisms 

 contained, except for the occurrence of a few living snails and speci- 



