1620 THE STORY OF THE UNIVERSE 



An insect, the Xylocopa violacea, related to the 

 humblebee, from which it differs in several anatom- 

 ical characters, and by the dark violet tint of its 

 wings, brings an improvement to the formation of 

 the shelter which it makes in wood for its larvae. 

 Instead of hollowing a mere retreat to place there all 

 its eggs indiscriminately, it divides them into com- 

 partments, separated by horizontal partitions. It is 

 the female alone who accomplishes this task, con- 

 nected with the function of perpetuating the race. 

 She chooses an old tree-trunk, a pole, or the post 

 of a fence, exposed to the sun and already worm- 

 eaten, so that her labor may be lightened. She first 

 attacks the wood perpendicularly to the surface, 

 then suddenly turns and directs downward the pas- 

 sage, the diameter of which is about equal to the 

 size of the insect's body. The Xylocopa thus forms 

 a tube about thirty centimetres in length. Quite at 

 the bottom she places the first egg, leaving beside it 

 a provision of honey necessary to nourish the larva 

 during its evolution ; she then closes it with a parti- 

 tion. This partition is made with fragments of the 

 powder of wood glued together with saliva. A first 

 horizontal ring is applied round the circumference 

 of the tube; then in the interior of this first ring a 

 second is formed, and so on continuously, until the 

 central opening, more and more reduced, is at last 

 entirely closed up. This ceiling forms the floor for 

 the next chamber, in which the female deposits a new 

 egg, provided, like the other, with abundant pro- 

 visions. The same acts are repeated until the retreat 

 becomes transformed into a series of isolated cells 



