544 PHILOSOPHY OF ZOOLOGY. 



ther, as to resemble paper. These external cases are termed 

 cocoons. The matter of which they are fabricated is pre- 

 pared by two long tubes, which take their rise in the abdo- 

 men, enlarge as they approach the head, and terminate by 

 a duct, which opens under the labium. By pressing the 

 orifice of this duct to one place, and then to another, the 

 larva draws out the tenaceous threads. 



The larvae that live in cells ready fabricated for their re- 

 ception, as the wasp and the bee, are not contented with 

 these as a covering during the pupa state, but they line 

 their sides and bottom, and cover their mouth with silk, 

 thus making a complete cocoon. These, after the insect 

 has been perfected, are left in the cell, and when it contains 

 another larva, a second lining is likewise prepared. Each 

 lining at the bottom, in the case of the bee, covers the ex- 

 crement, which the animal had produced in its larva state. 

 Hence, the walls of the bee-combs appear double or treble ; 

 nav, John Hunter, by whom the appearancfe was obser- 

 ved, has counted twenty different linings in one cell *. 



The external covering of the pupa, in some cases, con- 

 sists of pieces of earth or dried leaves, curiously joined to- 

 gether, and cemented by an adhesive secretion. 



After the insect has remained in a pupa state for a cer- 

 tain period, exceedingly different in the various tribes, it 

 bursts forth from its confinement in its state of maturity. 

 In this perfect condition it is termed the Imago. The or- 

 orans of reproduction now speedily enlarge, and preparation 

 is made to increase and multiply. 



The duration of the life of the pedate annulosa, in their 

 mature state, is confined in some to a few days, while, in 

 others, it extends to many years. Those which, like the 

 annual flowers, are destined to breed only once during life, 



• Phil. Trans. 1792, p. 193. 



