41 



neighbouring tree will be pulsating to a different time. This feature 

 has been observed of a European species of Luciola (though Mr. 

 Main and myself were unable to detect anything of the sort with 

 L. italica at Lugano), of an Indian lanipyrid, genus not stated, and 

 of the genus Aspiilofioiiia in South America. The American species 

 of I'hotiuuf! and Fliotiiris do not seem to possess the habit. 



The exact reason of this flashing in concert, or the method by 

 which it is brought about have not been ascertained. It has been 

 suggested that the light is not really intermittent in character, but 

 merely appears so owing to its being alternately masl\ed and ex- 

 hibited by movements of the creature's body, and that a slight puff" 

 of wind might perhaps affect all the members of a company and 

 cause them all to conceal their lights at once. Though this explan- 

 ation of the intermittent character of the light applies well enough 

 to Pi/ro/iliorux, an insect we shall shortly consider, it is certainly not 

 applicable to these Lanipyrid;e. It is true the light is not absolutely 

 extinguished between the Hashes, but it is so diminished as to become 

 practically dark ; moreover the Hashing in unison is too regular to be 

 caused by chance puff's of wind. A more probable explanation of 

 the phenomenon is that each flash exhausts the battery as it were, 

 and a period of recuperation is required before another Hash can be 

 emitted. It is then conceivable that the Hash of a leader might act 

 as a stimulus to the discharge of their tiashes by the other members 

 of the group, and so bring about the flashing in concert by the 

 whole company. 



The physical and chemical nature of the light of these insects 

 have been the subject of numerous investigations. Though often 

 spoken of as "phosphorescent," the light has nothing whatever to 

 do with the oxidation of phosphorus. 



The most recent conclusions are those of Dubois, and were 

 summarized by him in a communication to the Zoological Congress 

 at Monaco last year. He finds that the mechanism for the pro- 

 duction of light is the same throughout for both plants and animals, 

 and is the result of the action of an oxydising zymase upon an 

 organic proteid product m the presence of water. In the case of 

 luminous insects the proteid, which he calls hiciferine, is contained 

 in the form of granules in the photogenic organ, while the zymase, 

 to which he applies the name liiciferat<e is dissolved in the blood. 

 The light is given off' by the action of the luciferase on the luciferine 

 as the blocd passes through the luminous organs. This zymase can 

 be replaced experimentally by a chemical oxydizing agent such as 

 permanganate of potash, lead dioxide, hydrogen dioxide, etc. 



The luminous organs in these insects are found on dissection to 

 be abundantly supplied with tracheal which open by means of very 

 large spiracles. It is probable that by opening or closing these 

 spiracles the insect is able to regulate the supply of oxygen to the 

 luminous organs, and so in some degree to control the emission of 

 liijht. 



