345 



related family of free living worms known as Naididae was rejiresented 

 by small numbers of one or more undetermined species. 



The species of the genera Tubifex and Limnodrilus live in tubes 

 or burrows in the soft top ooze of stream bottoms, from which they 

 protrude the posterior end, waving it constantly when imdisturbfd, as 

 an accessory act in respiration. When very abundant these worms 

 literally carpet the bottom with a living naji of reddish brown or deeii 

 red. This fact is the more easily visualized by those who have not 

 seen them when it is known that they occurred in luiinbers as high as 

 fiO.OOO per square yard in upper Peoria Lake in the summer of 1922. 

 Such numbers amount to nearly 'J.jO rows of 250 each in such a space, 

 and call for a separation between individuals amounting to less than 

 fifteen-hundredths of an inch in each direction. 



The several times recorded occurrence of Tubifex tubifex in un- 

 usually septic situations in recent years by European writers, as about 

 the edges of septic tanks and very near the sources of the pollution 

 in sewage-fouled streams, seems to have led to the entire group being 

 referred to rather indiscriminately by local authors la ely as "slime 

 worms" or "sludge worms," with little or no reference at all to the 

 possible varying preferences or the identity of individual species. This 

 has been no doubt largely a result of the difficult and time-consuming 

 technique necessary in the determination of species in this group, and 

 the extreme rarity of specialists competent to render an opinion upon 

 them. Some of them occur quite frequently, however, in ordinary 

 clean bottom in our inland lakes and streams; and extensive carpets 

 of them have been observed near the edges of deep reservoirs thought 

 clean enough to be a part of the source of a city's water supply. Even 

 Tubifex tubifex has recently been reported by Muttkowski (1918) 

 from the bottom muds of Lake Mcndota; and was found, as repre- 

 sented by the American form as here understood, to be commonly 

 present in the comparatively clean nuids of thf Illinois River at and 

 near Havana in the early days of operations at the Illinois Biological 

 Station. 



Of the Tubificidae taken in upper Peoria L:ike in 1!)22 far the 

 most abundant one was not T. tubifex as might have been ex])ectcd on 

 the basis of recent .American and European records, but Lintiiodrilus 

 Iwffmeistcri. This worm occurred at twenty-one out of twenty-three 

 of the collecting stations in the ui)per lake, including all cross-sections, 

 and like T. tubifex and the undescribed species of Limnodrilus was 



