80 Pupa Stage of Insects. 
in use. Inside the pupa skin great changes are in progress, 
for either by modifying the larval organs or developing | 
parts entirely new by use of the accumulated material 
stored by the larva during its prolonged banquet, the won- 
Fic. 24. 
ab Eggs. Pupa. 
edef tate 4 Caps 
derful transformation from the sluggish, worm-like larva, 
to the active, bird-like imago is accomplished. Sometimes 
the pupa is surrounded by a silken cocoon, either thick, as 
the cocoon of some moths, or thin and incomplete as the 
cocoon of bees. ‘These cocoons are spun by the larvae as. 
their last toil before assuming the restful pupa state. The 
length of time in the pupa-stage varies from a few days to 
as many months. Sometimes insects which are.two-brooded 
remain as pup# but a few days in summer, while in winter 
they are months passing the quiescent period. Our cabbage- 
butterfly illustrates this peculiarity. Others, like the Hes- 
sian-fly and codling moth, remain through the long, cold 
months as larve. How wonderfulis this! The first brood 
