WINTER TENANTS OF OUR TREES. 51 



I can suggest. For one thing, cocoons temper the 

 rapid changes in the atmospheric temperatflre. A long, 

 steadily cold winter seems to be less destructive to the 

 enclosed pupce than a very changeable one of a lower 

 average temperature. Hence the value, in a changeable 

 climate, of such enswathments as help to graduate the 

 weather variations. 



Then, again, cocoons are of use in preventing the loss 

 of moisture by pupoe. For example, the pupa of a Ce- 

 cropia or Polyphemus moth exposed to the atmosphere 

 without its natural covering will, as a rule, dry up or 

 produce an imago which will not have moisture enough 

 in its tissues to properly expand its wings. 



Once more, cocoons conceal the inmates from their 

 natural enemies. If they be noticed they are seen not 

 to be edible, and the tough parchment enswathment 

 protects from any but a deliberate and vigorous siege. 

 Moreover, the odor of the pupa, by which many 

 enemies would be attracted to it, is probably largely 

 confined within the cocoon by their structure. You 

 must take my suggestions with some allowance, how- 

 ever. I confess that I am not in a position to be very 

 positive upon this interesting query, which involves 

 some puzzling and seemingl}' inconsistent facts. But to 

 return to our Cynthia cocoons, let me call your atten- 

 tion again to the manner in which the larva has 

 wrapped the leaf-stalks entirely around and carried the 

 windings clear up to the twig on which the leaves hang. 

 One is almost led to think that the worm wrought with 

 some knowledge that leaves have the habit of dropping 



