THE CANADIAN ENTOMOLOGIST. 359 



horny plates, which extend outward from either side of each segment. 

 These larvae (pen7isylvanica) appear to be semi-aquatic in habit ; at this 

 time of the year (early Sept ), while walking along the edge of Rock Creek, 

 in Rock Creek Park, Washington, D. C, numerous points of greenish light, 

 which glow slowly and then die out slowly, to glow again in a moment or so, 

 may be seen at the very edge of the water ; on investigation these proved 

 to be the larval forms of the Photuris clinging to moist stones, weeds, etc., 

 and presumably preying upon tlie small-r living things there. I noticed 

 one quite remarkable sight; looking over a bridge which spans the creek 

 just above a dam, one could see several of these points of light apparently 

 on the surface of the water, and within a radius of about five feet, glowing 

 and dying out again in their characteristic manner ; upon closer observa- 

 tion there appeared to be at least a hundred of these larvse thus apparently 

 floating. The current here is slow, but perceptible, and as the mass of 

 points of light did not change their position either with relation to each 

 other or with the bridge, they must have been clinging to grasses or stones 

 at the surface of the water. When compared at night in the same tube, 

 the light of the laiva oi pennsylvanica is distinctly more greenish than that 

 of the larva oi pyralis. 



The first time I saw the pennsylvanica in this neighbourhood, they 

 were flitting around the tops of some rather high trees, the flight being in 

 no particular direction. As seen there, they flashed with greater frequency 

 than the /jTrtZ/j ordinarily does, and the flash, instead of being a singl,' 

 prolonged emission, as in the latter insect, consisted of a series of several 

 short, brilliant flashes, which may be best described as a "twinkling." 

 This twinkling has often been observed since, and appears to be one of 

 the methods of light-emission most commonly indulged in by this species. 



Since this first observation, however, the pennsylvanica has been 

 observed to emit light in several other characteristic ways. The most 

 common of these, and probably the most common mode of light-emission 

 of this insect, consists of a single prolonged flish, about as long in dura- 

 tion, and about as frequently repeated as the dipping flish of \.\\^ pyralis, 

 delivered while the insect is flitting around bushes and the branches of 

 trees. The flash differs markedly from that oi \\iz pyralis. It begins as 

 a faint glow, rapidly increasing in brilliancy, until it attains an intensity 

 obviously much greater than that of the illu nination of the commoner 

 insect. It then ends suddenly, leaving an impression on the retina similar 

 to, but of course much less intense than that produced by a sudden flash 

 of lightning observed at night. As the maximum intensity of the light is 



