184 



cal distribution of the worms coincided with the vertical distribu- 

 tion of the "load" of the filter, since the greater part of the sludge 

 deposited at this time of year was confined to this zone, while below 

 it the stones were conspicuously cleaner. It seems very probable that 

 it is this feature of the situation which determined the distribution 

 in October, since these worms show a decided affinity for the sludge. 



These worms do not appear normally on the upper surface of the 

 filter bed, but may be found by removing the uppermost rock. The 

 physical conditions of this environment are as follows: the light is 

 practically excluded beyond the first six or eight inches ; moisture 

 is at a maximum, since large quantities of sewage are constantly 

 flowing down through the interstices; the temperature is cool and in 

 general fairly uniform for a given season; and an abundance of the 

 finer settling suspended matter finds lodgment on the surface of the 

 rock and in the interstices. 



The worms are distributed to the different parts of the plant by 

 the streams. They have a specific gravity slightly greater than water 

 and therefore sink slowly when placed in quiet water of some depth ; 

 but a stream of water will carry them when they are once loosened 

 from their hold on the supporting rock. The writer has observed in- 

 stances where several W'Orms had penetrated a mass of sludge which, 

 because of decomposition changes, had acquired a low specific grav- 

 ity, and when loosened from the point of accumulation, it floated 

 away, easily carrying the additional weight of the worms. 



Associated Animal Life. — These lumbricillid worms were not the 

 only animal forms present in the sprinkling filters. In fact, when 

 examined in October, it was found that there were other forms which 

 were more generally distributed and more abundant. No attempt 

 was made to list the microscopic life, and attention was confined to 

 the macroscopic forms, of which the following were the most com- 

 mon: Prorhynchns sp., small Neuiatoda (not identified), Pristina 

 sp., Nais sp., Hclodrilus suhruhicnndus Eisen, CoUcudwla (Isotoma 

 sp.), larvae and pupae of Psychoda albimacidata Welch and Chiro- 

 jwmidcr, and water-mites. 



COLOR OF LIVING SPECIMENS 



To the unaided eye, LuinhriciUus riitilus presents a general reddish 

 appearance. The region posterior to the clitellum appears uniformly 

 reddish, except that the ventral blood-trunk shows as a deeper red 

 line. The region anterior to the posterior margin of the clitellum 

 is distinctly lighter in color, and the region of X-XII in sexually ma- 



