LETTER OF JUNE 4TH, 1857. 7 



" which liberated small portions at a time from the constrict- 

 " ing part of the cocoon .... 



" I think the threads of the cocoon were ruptured by being 

 " brought in contact principally with the anterior portion of 

 " the mesothorax, for this was the most advanced part of the 

 " body when I first obtained a distinct view of the insect ; 

 " although just before the head and eyes, Avhich occupied a 

 " lower plane than the mesothorax, were finally extruded, 

 " several threads in contact with them were ruptured without 

 " causing the least injury to the eyes. The noise caused by 

 " the rupturing of the threads very strongly resembled that 

 " produced by the gnawing of a mouse. 



" The most remarkable part of the whole process Was the 

 " dilating force which the insect exerted by means of the 

 " wing-shoulders, for they were at once the means of ad- 

 " vancement in the process of delivery of the thorax and of 

 " dilatation of the apex of the cocoon. The entire muscular 

 " power of the thoracic muscles seemed to be concentrated 

 " energetically on the performance of this duty. After the 

 " dilatation of the resisting part of the cocoon, in which the 

 " thorax might be situated, the wing- shoulders appeared to 

 " be used as the points of support from which the meso- 

 " thorax was impelled against the resisting structures. 



" The entire thoracic case at this period is soft and flexible, 

 " and every effort after the insect was discernible was marked 

 " by an obviously increased breadth between the wing- 

 " shoulders and flattening of the convex surface of the 

 " thorax. I should state possibly, that I mean by the term 

 " ' wing-shoulders' that part where the nervures converge 

 " to become attached to the thorax. * * * The delivery 

 " was accomplished in about ten minutes after I first ob- 

 " served the movements within the cocoon, but I believe the 

 " entire time to be much more." 



I trust my description of this process is sufficiently clear 

 to enable you to understand it. I intended to submit it to 

 re-examination this season, but all my moths eluded my 

 vigilance. 



