LEPIDOPTERS: BUTTERFLIES. 



139 



a little tube, from which the caterpillar spins silken 

 threads. Two long slender bags within the body, 

 ending in the spinning tube, contain the material from 

 which the silk is made; this is a sticky fluid, which 







hardens into a thread as soon as it comes to the air. 

 Some caterpillars spin but little silk, others produce 

 it in abundance. Caterpillars change their skins about 

 four times in coming to their full growth as caterpil- 



