INSECT METAMOR PHOS I S 



The pupa has so many of the characters of the mature 

 insect that we might say it is self-evident that it is a part 

 of the adult stage, except that to say anything is "self- 

 evident" is almost an unpardonable remark in scientific 

 writing. However, it is clear to the eve that the pupa, 

 in casting off the skin of the larva, has entirely discarded 

 the larval form, except in certain insects that have a 

 larval form in the adult stage. The pupa may retain a 

 few unimportant larval characters, hut all its principal 

 organs are those of an adult insect in a halfway sta^e of 

 development. In studying the cicada, it. was observed 

 that the adult issues from the skin of the nymph in a very 

 immature condition. A careful dissection of a specimen 

 at this time would show that the creature is still imperfect 

 in many ways besides those which appear externally. By 

 very rapid growth during the course of an hour, however, 

 the adult form and organs are perfected. We have also 

 noted that with insects of incomplete metamorphosis the 

 adult is mostly formed within the nymphal skin some 

 time before the latter is cast off. The same thing is true 

 of a pupa. For several days before the caterpillar is 

 ready to molt the last time, it remains almost motionless 

 and its body contracts to perhaps less than half of the 

 original length. The caterpillar is now said to be in a 

 "prepupal" stage, but examination of a specimen will 

 reveal that it has already transformed, tor inside its skin 

 is a soft pupa in a preliminary stage of development 

 (Fig. 141 B). 



This first stage of the pupa of a moth or butterfly (Fig. 

 141 B) is entirely comparable with the immature adult 

 of the cicada formed inside the skin of the last stage of 

 the nymph (Fig. 141 A). The entire pupal period, 

 therefore, corresponds with the formative stage of the 

 cicada, which begins within the nymphal skin and is com- 

 pleted about an hour after the emergence. The only 

 external difference between the two cases is that the pupa 

 sheds its skin, making a final added molt before it becomes 



[153] 



