vu 



(3). Species with female apterous or with rudimentary wings; phos- 

 phorescence often very great in female, and frequently rudimentary in male ; 

 antennae generally rudimentary ; eyes large in the male, often occupying 

 nearly the whole head. [Pleotomus, Microjjhotus, Lampyris, &c.) 



Mr. Stainton asked how Mr. Gorhaiu had determined the intensity of 

 the light emitted by the insects which had been grouped in the manner 

 above referred to, since it appeared extremely difficult to say with certainty 

 whether one insect was more luminous than another without some actual 

 photometric measurement made upon the species when alive. 



Mr. Gorham stated in reply that the light-emitting segments at the 

 extremity of the abdomen were distinguishable by their white vitreous 

 appearance, and that he had considered the number and size of such 

 segments to indicate the phosphorescent power. He did not consider 

 that these vitreous segments were themselves luminous, but that the 

 source of light was within the body of the insect, and shone through the 

 transparent segments or could be withdrawn at pleasure. lu this manner 

 he thought the gradual extinction or intermittent flashing of the light might 

 be explained. 



Mr. Pascoe remarked that it was much to be regretted that Mr. Gorham 

 had not been able to observe the phosphorescence of some of the exotic 

 Lcojipyrido: in their native hal)itats, as he had no doubt that many of the 

 opinions now advanced would thus have to be considerably modified. 



Mr. W. C. Boyd asked how, on Mr. Gorham's view, the supposed source 

 of light could be withdrawn from the transparent segments, since the size of 

 the insects' bodies did not leave much space for such withdrawal? 



Mr. C. 0. Waterhouse suggested that the light-source might be with- 

 drawn into that portion of the body having opaque segments. 



Mr. M'Lachian, in connection with his idea of the supposed contem- 

 poraneous flashing of all the individuals in a swarm of LaiiipyridcB, called 

 attention to flies of the genus Argyra, which when flying exhibited at times 

 an appearance similar to tliat of small snow-flakes, owing to the silvery 

 pubescence with which part of the body was clothed, but which was observed 

 in certain positions, and especially when the insects rested, owing to the 

 pubescence being then concealed ; he thought this to some extent was an 

 analogous case to that of the light of swarms of Lampyridcc. 



Sir Sidney Saunders observed that the discussion involved two distinct 

 questions, — namely, the flashing at intervals and the simultaneous action of 

 large numbers in displaying their luminosity, — both of which he considered 

 as indisputable facts. As regards the first, he mentioned the circumstance 

 that when flying past, free from all obstructions, the Luciola suddenly 

 emits its light, and then remains untraceable until it repeats its flash at a 

 distance of some yards, and is therefore difficult to capture unless by over- 

 taking the fugitives and sweeping with a hat in the observed direction. 



