CORETHRA PLUMICORNIS. IS 

rating the carbons the Serrin light was extinguished, and the whole 
of the current sent through the Swan lamps, illuminating them as 
brightly as before. The reason that the Serrin lamp takes away 
nearly all the current from the Swan lamps is that its resistance is 
very much less. To charge the above battery, rather over half a 
gallon (1 Winchester quart) of strong commercial nitric: acid was 
required, and rather over 1 quart (; Winchester) of strong com- 
mercial sulphuric acid. The ordinary public would probably have 
to pay 6d.°or 7d. per pound for the former, and 2d. per pound for 
the latter. One charge is sufficient to work the above lamps well 
for one or two hours. I should not omit to state that Swan lamps 
can now be procured of 5 candle power, costing 5s. each. These 
would probably work well with 8 to ro cells. 
Experimenters must expect to incur considerable expense in 
broken Swan lamps. The slightest jar is sometimes sufficient to 
snap the carbon thread, and repair is, of course, impossible with- 
out destroying the vacuum. Finally, I may add that, as was to 
be expected, the light of the Serrin lamp exceeded that of the 
three incandescent lamps together, but there could be no com- 
parison as to steadiness and comfort. 
J. M. H. Munro, D.Sc. 

CORETHRA PLUMICORNIS. 
By Mr. A. C. BOwDLER. 
A Paper read before the Blackburn Field Naturalists’ Society. 
Order, DIPTERA.:.< 5. Family, CuLIciDé..:.... Genus, Corethra. 
HE Micrographic Dictionary names this insect, and refers to 
Kursalo’s monograph on Corethra plumucornis, and to other 
writers—Ray Lancaster, Pop. Sc. Review, 1865; Rymer Jones, 
Mic. Dy., 1866, page 99, and others. Its larva is so transparent 
that it is easily overlooked, although very generally distributed. 
It inhabits fresh water. Last year I obtained several specimens 
from a pool of water in a quarry at Ramsgrave, also from a pool 
near Ribchester. In February this year I found it very abundant 
in a small pond at Pleasington, and brought away some 40 or 50 
specimens. The head of the larva is small, and furnished with 
two remarkable looking hooks bent towards the mouth. The tail 
has a fan of hairs on the underside, which appear to act as a 
paddle. Its popular name is the Phantom Larva, and in Mr. 
Cooke’s “ Ponds and Ditches,” p. 208, there is asketch of it and a 
detailed description. The simplest plan of collecting the larva 1s 
by sweeping the water with a net, and they are then seen wriggling 
