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slide was used and a water trail was drawn lengthwise of it. A mass 

 of moist sludge from the filter stones was placed at one end and the 

 worms were placed at the other end. They followed the water trail 

 to the sludge, crawled around it and through it, and became quiet. 

 Bxperiinent 2. A circular cover-glass was supported on bits of filter 

 paper, water was run under it and a water trail was drawn from 

 it. Ten worms were placed at the end of the trail. The worms 

 followed the trail to the cover-glass but would not pass under it. 

 Experiment 5. The procedure was the same as in Experiment 2 except 

 that black paper was placed on the cover-glass the space under it 

 being somewhat darkened. The behavior of the worms was the same 

 as in No. 2. Bxperiment 4. The procedure was the same as in No. 

 2 except that a mass of sludge from the sprinkling filter was placed 

 under the cover-glass. In every case tried the worms passed under the 

 cover-glass in a short time, and after surrounding and penetrating the 

 sludge became quiet. 



It is not possible to explain, from the data, the behavior of the 

 worms with reference to the cover-glass in experiments 2 and 3. In 

 neither case did the worms pass under it, and in spite of the fact 

 that these forms are negatively phototactic, the area under the dark- 

 ened cover-glass in experiment 3 was avoided. There was evidently 

 some unknown factor present which was sufficiently active tO' over- 

 come the negative phototactic tendency of the worms and tO' prevent 

 their migration into more favorable light conditions. The experiments 

 show, however, a distinct recognition by the worms of the presence of 

 sludge and a positive reaction to it. Furthermore, it is evident that 

 this positive reaction is sufficiently strong to overcome the opposing 

 influence which prevented the worms from passing under the cover- 

 glass in experiments 2 and 3. The experiments showed also that the 

 positive reaction to the sludge was not due to negative phototaxis 

 since the worms did not pass under the cover-glass in experiment 3. 



Relation to the Sludge in the Sprinkling Filters. — That these worms 

 have a mechanical effect on the settling suspended matter which ac- 

 cumulates in the filters is readily seen. They are constantly burrow- 

 ing through the masses of sludge, and since they occur in such large 

 numbers they must play a prominent part in loosening up the sludge 

 and working it over, thus facilitating the oxidation of the unstable 

 organic matter. 



It has been observed at the Testing Station that during the winter 

 the sprinkling filters become clogged to a considerable extent ; that is, 

 in the Station parlance, they build their load by accumulating a large 

 quantity of sludge. This sludge is held in the filter until the tempera- 



