20 INTRODUCTION. 



insect, gorgeous in colouring, graceful in form, and 

 endued with high powers of rapid flight. The insect is 

 now in its imago or perfect state; with the exuviation 

 of the pupa-integument it has cast off all the vestiges 

 of the organs characteristic of the larva stage, and 

 assumed true legs, wings, compound eyes, antennie, a 

 more perfect nervous system, and most wondrous, 

 perhaps of all, the biting jaws of the injurious cater- 

 pillar have been metamorphosed into the delicate spiral 

 " tongue" of the nectar-sipping butterfly ! Not, how- 

 ever, immediately on emerging from the pupa-case is 

 the perfect insect ready to beat the air with its wings 

 and to fly where it listeth, for at first the wings are ^oft 

 and crumpled, hanging loosely at the sides of the body, 

 but after exposure for some little time to the air, and 

 when the tracheal system has by inspiration and expira- 

 tion become fitted for aerial flight, the insect sails awa}^ 

 and its wings, now possessing the necessary stiffness for 

 organs of impulsion in the air, are henceforth the crea- 

 ture's chief instruments as means of locomotion. In 

 cases of such a complete metamorphosis as these, there 

 is a wonderful dissimilarity between the larva and the 

 imago, and insects undergoing the three distinct changes 

 of larva, pupa and imago, are called "Holometabolous."* 

 But though complete metamorphosis obtains in the 

 majority of the Insect class, there are many kinds in 

 which the changes are partial and incomplete. In these 

 cases of semi-metamorphosis the larva bears some re- 

 semblance, more or less exact to the perfect insect, tlie 



* i.e., undergoing complete change, fioui o\oq "wliolc," and 

 IxBTajSoXi] " change." 



