164 NATURAL HISTORY. 



cocoon of fine silken fibers, and then others of coarser 

 texture, until the minute threads are formed into a ball 

 about the size of a pigeon's egg. These threads are 

 part "white, part yellow, very seldom green, and have 

 this peculiarity that instead of raveling or being tangled 

 like those of other caterpillars, they reel off easily. 

 After five days' spinning, the envelope is completed and 

 encloses the pupa ; at this time it is necessary, in order 

 to reel the silk, to expose the cocoon to such a degree of 

 heat as will kill the animal, because if allowed to remain a 

 perfect insect, before leaving its cell it discharges ^ sharp 

 fluid, which injures the quality of the silk, and prevents 

 it from beeing reeled. The silk culture now forms a 

 considerable branch of agricultural industry in France 

 and Germany, and is becoming yearly of more import- 

 ance in the United States. 



III. CREPUSCULARIA. LEPIDOPTERA. 



The bodies are cylindrical or conical ; antennas elon- 

 gated or spindle-formed, straight or curved; proboscis 

 mostly very long and slender ; wings either spread out 

 horizontally or roof-like. Caterpillars, slightly hairy ; 

 more frequently smooth ; with or without a horn ap- 

 pended to the tail. Metamorphosis takes place mostly 

 in a slight cocoon on the ground, in the pith of wood, or 

 in the air. They fly in the gray twilight of morning or 

 evening. 



1. THE HAWK MOTHS OR SPHINXES. 



The body cylindrical, feelers spread outwards, wings 

 roof-like and brilliantly colored. Caterpillar black, 



