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filters, and larg-e numbers are carried out in the effluents. The period 

 of maximum abundance is apparently rather short, but the worms are 

 abundant throughout most of the summer, beginning to diminish in 

 numbers as the autumn wanes. An interesting fact in connection with 

 the period of maximum abundance will be discussed in another con- 

 nection. No careful observations have as yet been made regard- 

 ing relative abundance in the different sprinkling filters. Girault 

 (June 22, 191 1 ) found them most abundant in sprinkling filter No. 5, 

 which is covered; but according to the observations of the Sanitary 

 Engineer there is usually at that time of year an abundance in all the 

 sprinkling filters except No. 3. 



During the writer's investigations at the Testing Station (Oct. 5- 

 25) a careful examination of all of the tanks, settling basins, and sprin- 

 kling filters was made with the view of determining the distribution 

 of the species at that time of year. It was found that the worms 

 were confined to certain of the filters and their effluents. While the 

 greatest abundance occurred in No. 4, a few were found in Nos. i and 

 5, and some in the general filter effluent. Various considerations were 

 found to throw light upon the facts of distribution. Absence of these 

 womis in the septic tanks is, no doubt, due chiefly to the absence 

 of dissolved oxygen and the presence of inimical gaseous decomposi- 

 tion products. Absence in the settling tanks is due probably to the 

 very low dissolved oxygen content. Absence in sprinkling filter No. 

 2 can be accounted for by the fact that the influent of this tank comes 

 directly from the modified Dortmund tank, where considerable sul- 

 phate reduction occurs, its effluent being laden with hydrogen sulphide 

 which is harmful to animal life, not only because it diminishes the 

 available oxygen but because it is itself poisonous. The appearance 

 of the worms in sprinkling filters Nos. i, 4, and 5 is presumably due 

 to the fact that the influents of these sprinkling filters are effluents of 

 the settling tank and are "fresh." The great abundance in No. 4, as 

 compared with the scarcity in Nos. i and 5, in October, seemed to be 

 due to the fact that No. 4 contained an unusual amount of sludge 

 for the time of year, while the quantity of sediment on the stones in 

 Nos. I and 5 was decidedly smaller. The reason for the appearance 

 of the worms in the sprinkling filter effluents is a purely mechanical 

 one, since they are carried there by the descending currents of sew- 

 age. 



The vertical distribution of the worms in the sprinkling filters 

 during the summer is not known; but an examination of No. 4 in 

 October showed them to be largely confined to the upper two feet of 

 the filter bed. Below that limit they occurred but rarely. This verti- 



