288 THE WONDERS OF INSTINCT 



they go down into the ground, but not very far. In my 

 rearing-jars, which are supplied with fine and very loose 

 earth, they descend to a depth of three or four inches at 

 most. I dig up a few in mid-winter. I always find them 

 carrying their faint stern-light. About the month of 

 April they come up again to the surface, there to continue 

 and complete their evolution. 



From start to finish the Glow-worm's life is one great 

 orgy of light. The eggs are luminous; the grubs like- 

 wise. The full-grown females are magnificent light- 

 houses, the adult males retain the glimmer which the 

 grubs already possessed. We can understand the object 

 of the feminine beacon; but of what use is all the rest 

 of the pyrotechnic display? To my great regret, I 

 cannot tell. It is and will be, for many a day to come, 

 perhaps for all time, the secret of animal physics, which 

 is deeper than the physics of the books. 



