OBSERVATION OF INCOMPLETE METAMORPHOSIS. 37 



four molts, while others shed their skin twenty times 

 or more. 



It is at the time of molting that changes in the 

 form of the body take place. 



Fig. 17 represents the cast skin of a nymph of a 

 dragon-fly. 



LESSON XV. 



OBSERVATION OF INCOMPLETE METAMORPHOSIS. 



1. Collect a considerable number — fifteen or twenty 

 or more — of nymphs of locusts or crickets, and place 

 them in a breeding cage. See page 327 for directions 

 for making inexpensive breeding cages. 



2. Put a sod of growing grass in the cage for the 

 insects to feed upon, and replace it with a fresh one 

 when necessary. 



3. Endeavor to rear the nymphs, and make notes 

 on their changes. 



4. Examine the cage daily, and when cast skins 

 are found, study them and preserve specimens for 

 your collection. 



5. Preserve a specimen of each of the nymph 

 stages, and label it with the date on which it was 

 taken. 



6. Observe that, although the changes between 

 the different nymph stages are slight, the change be- 

 tween the last nymph stage and the adult is a marked 

 one, there being a great increase in the size of the 

 wings at this time. 



