34 



BEES AND BEE-KEEPING. 



tube by any bending of the body of the insect, just 

 as the spiral wire within indiarubber gas-piping secures 

 a constant flow of gas, in spite of any twisting of 

 the pipe itself. The embryology of insects has shown 

 that the tracheae are developed by invagination (a turn- 

 ing inwards) of the outside skin (precisely as the 

 bowel is formed in the larva, see Fig. 13), and that, at 

 the time of moulting, the tubes in the neighbourhood of 

 the spiracles are cast off. That this is true in the bee 

 is easily proved by those having a microscope of even 



Fig. 7.— Part of Exuvium of Bee Larva (Magnified 100 times). 

 sp, Spiracle; tr.l, Tracheal Lining. 



moderate capability. Lifting from a cell a half-crown 

 larva, a little transparent mass will be observed upon 

 the centre of the cell base, which mass to some extent 

 filled the cavity formed beneath the body as the orub 

 lay head and tail together. This is found to contain 

 one or more cast skins, which carry with them the 

 covers of the spiracles. The investing membrane 

 (Fig. 7) of the contiguous tubes is withdrawn, while 

 the tiny hairs and scales of the body also lose a layer 

 as we see by the illustration. It is difficult to under- 

 stand how the extremely thin lining of the tracheae is 



