185 



ture specimens shows a distinct white spot with no trace of red. The 

 surface laver of the limestone rock composing the sprinkhng fiher 

 beds ac([iiires after a time a reddish brown color, due partly to the 

 formation of certain ferrous compounds, and with this sort of a back- 

 ground it is often a little difficult to distinguish the worms ; but the 

 white spot on X-XII is more or less conspicuous, and soon, if not 

 at once, reveals their presence. When large numbers arc placed in 

 water they often accumulate in a compact miass, and in such an ag- 

 gregation the red color seems to be intensified, the whole mass giving 

 one the imiircssicm of a deeper red than docs a single isolated indi- 

 vidual. 



Examination under magnification shows that the body is some- 

 what translucent and of a light yellowish tinge, the red color being 

 really due to the blood of the vascular system, since the translucency 

 of the body wall permits the vascular system to show through boldly 

 enough to determine the external appearance. The principal vessels 

 and their connecting branches can easily be traced, and the pulsations 

 of the dorsal vessel may be watched with ease. The white spot in the 

 region of X-XII is due to the presence of developing reproductive 

 elements, and constitutes external e\idence of the sexual maturity of 

 the specimen. 



I.OCOMOTION 



The sole mode of progression is a fairly brisk crawling on a 

 supporting surface. A number of experiments were performed with the 

 view of determining the relative efficiency of this mode of locomotion 

 on different surfaces. Specimens were tested with the following sub- 

 stances(both dry and moist) as supporting surfaces: filter rock, sludge, 

 wood (planed surface), ground glass, smooth sheet-iron, and smooth 

 glass. Results showed that the efficiency of the crawling was very 

 much higher on all of the surfaces when they were moist, dry sur- 

 faces being an important hindrance to dispersal, and that the degree 

 to which the moist surfaces of the above-named substances favored 

 efficiency of locomotion varied approximately in the order indicated 

 in the list, the maximum occurring on the filter rock and the mini- 

 mum on smooth glass. The worms crawl with considerable ease over 

 the surfaces of the rock in the sprinkling filter beds, and owing to 

 the irregular shapes of the pieces the interstices form a continuous 

 series of chambers and passages abundantly supplied with sewage 

 and settled solids, through which the worms pass easily. They also 

 have a surprising ability for working their way through the masses 

 of sludge which accumulate on the surfaces of the stone. On a moist 

 ground-glass surface the worms make moderately efficient progress, 



