GROWTH AND TRANSFORMATION 191 



the vast majority of insects when adult, has an important 

 if indirect bearing on reproduction, as it facilitates a wide 

 range over localities suitable for egg-laying, and thus tends 

 to bring about an increase of the area occupied by the 

 species. 



It has been noticed that in the growth of insects generally 

 there is something of a crisis at the penultimate stage of the 

 life-history, and this becomes especially evident in the 

 development of those insects, the vast majority of the class, 

 that undergo complete transformation with a resting pupal 

 stage between the end of the larval and the beginning of the 

 adult hfe. The nature and meaning of the pupa has always 

 presented a fascinating problem to students of the biology of 

 insects. The Greek philosopher Aristotle regarded the 

 insect pupa as a second egg, and William Harvey (1666), 

 taking a similar view, suggested that the amount of food- 

 material in a butterfly's egg is insufficient for the building 

 up of so highly organised a being as the parent, and so only 

 the imperfect caterpillar can be hatched from it ; the cater- 

 pillar after weeks of feeding stores up the necessary amount 

 of food and then reverts to the condition of a second egg 

 (the pupa), whence the butterfly in due time may be hatched. 

 A superficial examination of the hard, egg-shaped 

 puparium of a bluebottle or the brittle cocoon wherein rests 

 the pupa of an " eggar " moth might be thought to afford 

 countenance to such a view. But even in the obtect pupa 

 of a butterfly, with its wings and appendages closely adherent 

 to the body, many of the organs of the perfect insect can be 

 clearly recognised, and much more is this the case in the 

 " free " pupa of a beetle, lacewing, or wasp, in which the 

 wings and limbs stand out from the body in much the same 

 way as they do in the adult. The envelope of the actual 

 pupa, therefore, is clearly the cuticle of the insect itself, 

 even though, in the case of an obtect pupa, it is specially 

 modified in correspondence with what is predominantly a 

 passive stage in the life-history. 



Examples have already been given of exopterygote insects 

 such as cicads, and scale-insects, in which the penultimate 



