20 



ELEMENTARY STUDIES IN INSECT LIFE 



FIG. 21. The de- 

 veloping chrysalis 

 of the black swal- 

 lowtail. Discarded 

 larval skin, mue^i 

 wrinkled, still on 

 FIG. 20. Caterpillar of black swallowtail about lower part of body. 



to shed the last larval skin. Enlarged to show Photographed from 



"cushion" and "silken loop." Photographed 



from life. 



state the insect remains suspended for from nineteen 

 to thirty hours. 



At the end of this resting period the whole body 

 begins to contract, expand, and twitch; the skin has 

 become thin, old, and almost imperceptibly begins to 

 move backward, gathering in tiny folds ; it breaks on 

 the back along the median line of the thorax. The body 

 movements increase, the central portion elongates, the 

 thorax rests back heavily npon the silken loop. The 

 whole covering, the feet, the head, all appendages are 

 discarded from the posterior end, which is loosened 

 momentarily for the purpose. The caudal end is again 



