88 THE AMERICAN MONTHLY [May, 



regarded as their defensive coating. The fresh-water sponges may be fre- 

 quently found in rapid running water, attached to large loose stones, or the 

 under side of timbers. They are also found on water-logged or floating tim- 

 ber and submerged stumps, and many of the species grow in deep water from 

 ten to twenty feet or more below the surface. The fresh-water sponges are 

 widely distributed. So far as known, most of the species prefer pure water, 

 biit some of them have been found to flourish in water unfit for domestic use. 

 Their presence has been known to give water a very disagreeable odor and taste, 

 as was especially noticeable at Boston in 1881, when it was found that a large 

 quantity of decomposing sponge in one of the reservoirs was the cause of the 

 trouble. Nevertheless, the fact that they exist in a public water supply need 

 not be the cause of serious apprehension. It is not known that they have ever 

 been the direct cause of disease. 



Several rhizopods have been identified in filterings from the city mains, and 

 of this class of life it can only be said that they must be taken when present 

 in any quantity as indicating considerable impurity. Their natural habitat 

 is to be found in the ooze along muddy borders and in the intei^stices of sphag- 

 num growing in the margins of swamps. As a general statement, it may be 

 said, therefore, that they are never found in quantity in waters about the puritv 

 of which there is no question. As yet only a small number of idiizopods have 

 been seen in Hemlock lake water, but a study of the swamp at the south end 

 of the lake would doubtless reveal a considerable colony of them. 



Something like twenty species of infusoria are known to exist in Hemlock 

 lake water as received at Rochester, and some of these are found in con- 

 siderable numbers in nearly every filtering. Probably the most numerous, 

 both as to number of individuals and species, are the Vorticclli^ . Eiiglena 

 has also been seen a few times in considerable quantitv- Para/nechuJi has 

 been seen a few times in considerable quantity, but usually this representative 

 filth infusorian is not found in fresh filterings. It is only after the filtering 

 has stood and become stagnant that paramecium appears. Two species of 

 Stentor have also been observed, but never in quantity. Cerathim loitgi- 

 corne and Peridininm tabulatum are two interesting infusorians found at 

 times in vast quanties. Trachelocera olor is another filth infusorian occa- 

 sionally seen. Amphileptus anser is also found usually among decaying 

 vegetation. The other species of infusoi ia have thus far been found only 

 occasionally. The presence of any considerable amount of infusoria must 

 be taken as indicating serious contamination. 



Of fresh water polypes, we have the two common species of hydra, namely, 

 Hydra vulga7-is and Hydra viridis. The natural habitat of the hydra is 

 ponds, ditches, and any slow running and stagnant water. Their food is 

 chiefly the smaller species of entomostraca and infusoria among living animals 

 and probably any small particles of organic matter which may be present. 

 When in confinement they have been known to thrive on shreds of fresh meat. 

 Their presence in any quantity must be taken as indicating a considerable 

 degree of impurity. 



Of entozoa we find the common Anguilhila Jluviatilis^ and it is supposed 

 that the ova oi Ascaris lumbricoides have been seen. This worm is the well- 

 known parasite of the human intestine. It is also a parasite of some of the 

 domestic animals, as for instance the hog, and the probability of its presence 

 may be inferred by considering the nature of the contamination about Hem- 

 lock lake. 



Of the annelida, we have recently identified a few specimens of the dis- 

 gusting Tubifex rivulorum^ a reddish transparent worm whose natural 

 habitat is in the banks of mud deposited from flowing sewage. In the eastern 

 part of the city there are several streams whose flow in dry weather is almost 



