Il6 ENTOMOLOGY 



rays, the remainder being heat or chemical rays, of no value for illumina- 

 ting purposes; while the light-giving efficiency of the electric arc is only 

 ten per cent, and that of sunlight only thirty-five per cent. The luminous 

 efficiency of the firefly is, however, not much under one hundred per 

 cent.; in Photuris pennsyhanica it is about ninety- two per cent., accord- 

 ing to Coblentz an efficiency as yet unapproached by artificial means. 

 The actinic power of the light is so slight that it affects a photographic 

 plate only after a long exposure. Coblentz, who has applied most 

 refined methods of measurement to the radiation of fireflies, found 

 that exposures of one to five hours were necessary with the spectro- 

 graph. He was unable to detect any infra-red radiation; the thermal 

 radiation, if present, being immeasurably small as yet. The intensity 

 of the glow averages ;H3o>ooo candle power in our common fireflies, 

 according to Coblentz. 



This luminosity serves to bring the sexes together. "The male flies 

 over the tops of the grasses, weeds, etc., dropping down between them 

 and flashing; any females that come within the range of his flash, answer 

 by their slower flash; if the male sees this answering flash from one, he 

 approaches her, flashes again, to which she answers, and he then finally 

 locates her definitely by means of subsequent flashes," as McDermott 

 says. He found that he could get responses from the females by imi- 

 tating the flash of the male with a small electric bulb or even with a com- 

 mon safety match, and that he could deceive the males also by flashing 

 the tiny electric light after the manner of the female. 



Synchronism/ Several observers in the Philippines and East 

 Indies have seen the phenomenon of thousands of fireflies flashing 

 exactly in unison; all the fireflies in the same tree, for example, flashing 

 simultaneously (105-109 flashes per minute, in one instance), with regular 

 intervals of darkness. This rare phenomenon, to which Professor E. S. 

 Morse called attention, has attracted considerable interest in the 

 columns of Science. There seems to be no doubt as to the accuracy of 

 the observations, but an explanation as to how the synchronism is 

 effected and regulated is still lacking. The phenomenon can hardly be 

 due to chance when thousands of individuals are involved. The 

 fireflies referred to, in Siam and the Philippines, belong to the genus 

 Calaphotia (0. A. Reinking). 



9. RESPIRATORY SYSTEM 



In insects, as contrasted with vertebrates, the air itself is conveyed to 

 the remotest tissues by means of an elaborate system of branching air- 



