LEPIDOPTERA. 231 



a slit in the first segment of the body just behind the head, a 

 pair of soft orange-colored horns, growing together at the 

 bottom, and somewhat like the letter Y in form. The horns 

 are scent-organs, and give out a strong and disagreeable smell, 

 perceptible at some distance, and seem to be designed to 

 defend the caterpillars from the annoying attacks of dies and 

 ichneumons. These caterpillars usually come to their full 

 size between the tentii and twentieth of July, and then 

 measure about one inch and a half in length. After this, they 

 leave off eating, desert the plants, and each one seeks some 

 sheltered spot, such as the side of a building or fence, or the 

 trunk of a tree, where it prepares for its transformation. It 

 first spins a little web or tuft of silk against the surface 

 whereon it is resting, and entangles the hooks of its hindmost 

 feet in it, so as to fix them securely to the spot ; it then proceeds 

 to make a loop or girth of many silken threads bent into the 

 form of the letter U, the ends of which are fastened to the 

 surface on which it rests on each side of the middle of its 

 body ; and under this, when finished, it passes its head, and 

 gradually works the loop over its back, so as to support the 

 body and prevent it from falling downwards. Though it 

 generally prefers a vertical surface on which to fasten itself in 

 an upright posture, it sometimes selects the under side of a 

 limb or of a projecting ledge, where it hangs suspended, nearly 

 horizontally, by its feet and the loop. Within twenty-four 

 hours after it has taken its station, the caterpillar casts off its 

 caterpillar-skin and becomes a chrysalis, or pupa, of a pale 

 green, ochre-yellow, or ash-gray color, with two short earlike 

 projections above the head, just beloAV which, on the upper 

 part of the back, is a little prominence like a pug nose. The 

 chrysalis hangs in the same way as the caterpillar, and remains 

 in this state from nine to fifteen days, according to the 

 temperature of the atmosphere, cold and wet weather having 

 a tendency to prolong the period. When this is terminated, 

 the skin of the chrysalis bursts open, and a butterfly issues 

 from it, clings to the empty shell till its crumpled and drooping 

 wings have extended to their full dimensions, and have become 



