A NATURALIST IN BRAZIL 



control of the nervous system. The rhythmical appearance and 

 disappearance of the light, which is seen in the Indian fireflies 

 also, is due to the movement of the terminal segments, which now 

 conceal the luminous plates and now uncover them. The function 

 of this rhythmical illumination is to attract the attention of other 

 fireflies ; just as in the streets of our cities the luminous advertise- 

 ments catch the eye by continually appearing and disappearing. 

 It may also afford the insect a measure of protection, for it has been 

 observed that the Carabid beetles leave the fireflies alone. A frog, 

 however, would not be intimidated by their light, which would only 

 draw his attention to his prey. 



But besides the small fireflies, there are in Brazil much larger 

 luminous beetles, which belong to quite a different family, namely, 

 to that of the Elateridae (Plate 29, II, 8). I was once sitting on the 

 verandah of a lonely house in the forest of northern Pernambuco, 

 when such a beetle came flying up ; it had two greenish-blue lanterns 

 on its shoulders, so that it seemed, like a locomotive, to be lighting 

 its own track. It was a magnificent sight : especially when more of 

 these living aerial locomotives came floating up and flying across 

 the verandah. I have caught such luminous beetles, some species of 

 which have a third light on the underside of the body; even by 

 daylight the luminous organs were perceptible as yellow spots on 

 the hinder edge of the brown scutum or neck-shield, and they 

 blazed up at once if I carried the long narrow beetle into the dark. 

 I always kept such a "cucujo," as the insect is called in the West 

 Indies, in a glass on my bed-table, so that I might be able to tell 

 the time in the night. It filled the whole room with a faint green 

 light, which was intensified if I shook the glass. The explorer Dubois 

 succeeded in isolating the luminous substance of the "cucujo," and 

 he ascertained that it gave less than one-four-hundredth part of the 

 heat given off by a Bunsen flame of the same candle-power, 

 Wasmann facetiously suggested that it might one day be possible 

 to prepare pills of "cucujin," which scholars might swallow in order 

 to be able to work by the light of their own bodies. I have been told 

 that burglars have sometimes rubbed their faces with the green 

 luminous substance, in order to frighten the inmates of the house 

 they were entering. In 1634, when Sir Thomas Cavendish and 

 Sir Robert Dudley, in command of the English fleet, proposed 

 making a landing in the West Indies, they saw innumerable lights 

 moving about on the shore, and drew off again, concluding that the 

 Spaniards were approaching with an army of torch-bearing soldiers. 

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