250 



TRANSACTIONS OF THE ILLINOIS 



a difficult problem to decide. Cabbage is capable of surviving very 

 severe cold, and hence we presume is a native of a northern climate ; it 

 is therefore possible that it communicated this property to the worm 

 which feeds upon it. 



When it has completed its growth, admonished doubtless by some 

 peculiar feeling that it is about to undergo a change, it becomes uneasy 

 and commences running to and fro seeking some place of retirement where 

 it may safely pass the pupa or chrysalis state. For this purpose it selects, 

 if it can be found, some place above ground, and that is somewhat pro- 

 tected, as the under side or margin of a rail, board or projecting substance, 

 apparently preferring dry, woody substance. I have observed them climb- 

 ing the sides of a two-story house to the eaves before content with the 

 position. Having found a place that is satisfactory, the first act of the 

 caterpillar is to spin a little mat on the surface, in which it can fix the 

 booklets of its feet as a means of support. It next spins a strong silken 

 cord across the middle of its body, fastening it firmly on each side to the 

 plank or rail on which it is placed. Soon after this operation is through 

 the worm commences contracting in length, especially its anterior portion; 

 the color also changes from the bright green to a dull or dirty yellowish- 

 green, approaching more and more to the dull gray of the pupa. The 

 outer skin during this time is loosened from the pupal skin within, which 

 by this time is completely formed; it now gives way to the pressure of 

 the insect within and splits open along the head and front part of the 

 back. The pupa proper now appears, and having relieved itself of the 

 old larval skin, assumes the chrysalid form of the species. 



The pupge vary in color not only according to age, but after they 

 have fully completed their pupal growth ; almost every color from a dull 

 yellowish-green to an ash-gray may be encountered. A light gray with 

 numerous black points appears to be the most common ; those which are 

 parasitized are paler than those that are living. The length varies from 

 about .70 to .80 of an inch; a perfect one now before me measures 

 exactly .75 inch, the precise measurement given by Dr. Fitch as the usual 

 length. The angles in the thoracic region are sharp and somewhat lami- 

 nated, the two anterior lateral ones presenting a single prominence, the 

 posterior ones two prominences; the anterior end is armed with a short 

 spine which projects forward. 



The length of time that the summer brood remains in the pupa state 

 varies considerably. Dr. Fitch gives the length of time which six speci- 

 mens of the summer brood remained in this state, partly from his own 

 observations and partly quoted from the statement of Joseph L' Admiral, 

 as follows : 



ENTERED PUPA STATE. BUTTERFLY APPEARED. LENGTH OF PUPA STATE. 



July 8 July 19 ii days. 



" 20 August 5 16 " 



August 19 " 26 7 " 



" 22 September 2 11 " 



" 29 " 7 9 " 



September 4 " 23 19 " 



