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organs and the latter in the blood, and the entry 

 of blood into these organs produces the manifesta- 

 tion. It may be pointed out, however, that neither 

 of these explanations will account for the luminosity 

 of the egg, where there are neither air-tubes nor 

 blood-vessels. 



Whatever be the true explanation of its chemistry, 

 it is certain that the exhibition is under the control 

 of the insect, as may be proved on capturing an 

 individual. Gilbert White was of opinion that the 

 Glow-worm puts out her light between eleven and 

 twelve o'clock at night ; and although no modern 

 observer appears to have taken the trouble to 

 check this statement, it is quite probable, for 

 many nocturnal insects have definite hours of 

 flight, and if the male Glow-worm ceases to fly 

 about that hour one might expect the female to 

 conserve her light by switching it off at the time 

 when the experience of the race has proved it to 

 be ineffectual. This, of course, presumes again 

 that the light is of sexual importance. 



On this point, as to the reason for the lumines- 

 cence, it should be mentioned that Mr. Belt 

 contended that it was protective. He found that 

 the insects were distasteful to insectivorous mammals 

 and birds ; and, therefore, it would be an advantage 

 to the species that their enemies should be able to 

 recognize them at once by their light, and so avoid 

 them. This explanation, however, does not go 

 far enough. 



It is not generally known that the Glow-worm 



