on Bomhylii at Pompeii. 499 



On looking about to see what was the cause of this noise, 

 I immediately perceived that the whole area was swarming 

 with great numbers oi Bomhyliiis medius, which were flying 

 about all over the surface (not hovering in the air), care- 

 fully examining every crevice and hole. With them were 

 an equal number of a large species of Andrena (of which 

 I was not able to capture a specimen), engaged in making 

 the burrows for their nests ; and it was evident that the 

 Bomhylii were engaged in finding out the already-provi- 

 sioned nests in which to deposit their eggs. Fortunately 

 I also discovered (sticking nearly out of the ground) the 

 exuvia of a pupa of the Bombylius, just in the same 

 manner as the cast pupa skin of a Cossus or Zenzej'a is 

 seen sticking out of the trunks of trees, or still more 

 closely as the pupa of a Hepialus or Tipula, which are 

 often found partially exserted above the surface of the 

 ground, the pupa of the Bombylius being thus shown to 

 have the instinct to force its way to the siu'face of the 

 ground before assuming the imago state, by the help of the 

 numerous spines with which the segments of the body are 

 dorsally armed, and which, being directed backwards, 

 allow the insect to Avork upwards and prevent it, in its 

 advancing progress, from slipping backwards. 



