EXAMINATION OF THAMES WATEE. 753 



earthworm. Amongst other larvae which abound in 

 Thames water are the well-known blood-red Thames 

 mud-worm. This worm is familiar to Londoners, as it 

 not only finds its way into cisterns, but is frequently 

 observed during the summer months covering the mud- 

 banks at low water, and imparting to the mud a deep 

 blood-red colour. The presence of mud-worms cer- 

 tainly indicates a dangerous contamination; their 

 favourite breeding-haunts being the sewage-polluted 

 mud-banks of rivers. The larvae of the genus Culi- 

 cidae, especially that of Chironomus viridulus (fig. 8) 

 a very minute species of the gnat tribe, are at cer- 

 tain periods numerous. This larva, unlike most other 

 species, builds up a brown tubular case, which it 

 anchors to the bottom or side of the bottle. Therein 

 it very quietly secretes itself. In a few days' time its 

 larval stage is completed, and it becomes transformed 

 into the imago, and towards evening, just as the sun is 

 declining, it quits its dwelling and floats up to the sur- 

 face of the water, and, having fairly balanced itself, it- 

 spreads its gossamer wings and flies away. The head of 

 the male is surmounted by a pair of plumose antennae, 

 which are long and delicate. The body is of a pale 

 green colour, apparently destitute of scales or feathers, 

 a well-known characteristic of Culicidse. All the gnat 

 tribe, inclusive of the dreaded mosquito of the tropics,, 

 lurk and thrive in malarious and fever- stricken locali- 

 ties. The eggs of Chironomus viridulus are extremely 

 minute, about the l-100th of an inch in size (fig. 7). 

 It may be remarked of gnats, that, like vultures, they 

 are bred amongst carrion. 



As usual, the smaller crustaceans, entomostraca, &c., 

 are found in large numbers in Thames water. 1 In 

 warm weather, and as soon as the temperature of all 

 river- water reaches 60 Fahr., Daphnia pulex increase 

 with amazing rapidity, and if swallowed may produce 

 diarrhoea and dysentery. In Boston, America, the water 

 at one time was much infested by water-fleas, and the- 

 consumers of the water suffered from fatal attacks of 

 Bummer cholera. At Dorpat, Sweden, an epidemic 



(1) See a paper by the author in the English Mechanic, April 30, 1880. 



3 c 



