GLOW-WORMS, TERMITES, SHELLS 231 



There seemed to be nothing peculiar in the conditions 

 of the atmosphere. Clouds hung about the hills, and 

 there was a sensation of impending rain. But this is 

 scarcely sufficient to account for such a uniform effect. 

 Whatever may be the original cause of the phe- 

 nomenon, I think there can be little doubt that 

 it is of real value to the propagation of the species. 

 No one has shown with greater force than Darwin 

 how dangerous are the effects of close interbreeding 

 and how marked is the improvement in both vigour 

 and fertility that follows on the union of different 

 strains. This, 1 think, must be the object that Nature 

 has in view. It secures the special benefits of fertiliza- 

 tion that follow on the union between different nests. 

 For this reason all emerge at the same time and 

 intermingle in one common stream. We can seldom 

 understand how Nature works ; we can only wonder 

 at the results that she attains. 



The shedding of the wings is an extraordinary 

 phenomenon. It takes place so suddenly, all four 

 wings at the same moment, that it looks as if it were a 

 premeditated and voluntary act on the part of the insect. 

 I do not think that this is the case, for if the insect is 

 decapitated and the brain thus removed, the wings will 

 still fall off. Nor is the flight through the air or the 

 vigorous vibration and flapping of the wings which 

 the insect makes after alighting in any way necessary, 

 for I find that, if an insect is captured before flight 

 and confined beneath a watch-glass where it can 

 scarcely move, the wings will still come away. The 

 act is hastened by any sudden stimulus. Decapita- 

 tion, puncturing the thorax, even mere handling of 

 the insect, may cause the wings to be cast off. 



