VII1] Introduction to Insects 91 
insects may be derived from putrefying matter may 
easily be shown to be wrong by keeping such material 
as putrefying meat so that insects cannot get near it. 
If however the meat is kept so that insects can reach it, 
Fig. 28. A cabbage leaf bearing the cocoons of an ichneumon 
wasp. (These cocoons are falsely called caterpillars’ eggs.) 
they will lay their eggs there, and from these maggots 
will be formed, and eventually flies. 
The passage through these changes from the time 
they are laid as eggs until they become winged forms 
is known as the transformation or metamorphosis of 
insects. Three different stages of metamorphosis are 
found in all butterflies and moths and also in a large 
number of other insects. 
