76 ENTOMOLOGICAL NEWS. [Mar., '07 



the last time it began to spin the button of silk, and then, al- 

 though its position was reversed, it continued spinning for 

 an hour, and finally attached itself. 



After the spinning was completed, the larva turned slowly 

 around and felt about carefully with the posterior end until it 

 came into contact with the mound of silk, when, with a deft 

 'motion, the hooks of the anal prolegs were inserted and twisted 

 firmly into it. Thus it is seen that the stimulus which impels 

 the reversed position during the spinning really anticipates an 

 upright position for the pupa. 



After a short period of rest the larva began to spin its girdle. 

 This was accomplished exactly as by Pieris rapae L. The 

 head and thorax are bent sharply backward and the thread is 

 attached at one side of the body. Keeping the anterior end 

 in this flexed position, it carries its head by torsion to the 

 opposite side, where the thread is again attached. Back and 

 forth it keeps spinning, strand by strand, until the girdle is 

 strong enough to support the pupa properly. Two specimens 

 were observed, and the one spun 24 strands, the other 33. 



Thus the girdle spans twice the diameter of the body, and 

 perfect allowance is made for the increased diameter of the 

 pupa. When the spinning of the girdle is completed, which 

 takes from 20 to 25 minutes, the head is slowly and care- 

 fully withdrawn from the loop of silk. On the following 

 day, May 26th, about 3 P. M., the pupa emerged. 



The entire larval period, then, is from 12 to 14 days 

 in the laboratory, some growing faster, others slower, than 

 the one described above. But in the field the period seems 

 to be longer. On May 12th no larvae were to be seen on 

 any of the food plants, and on May 26th, the same day 

 pupation occurred in the laboratory, the larvae in the field 

 were in all stages from the second to the beginning of the fifth 

 instar. Assuming that other eggs of the same age as those 

 collected were left in the field, the larval period must be 

 several clays longer than in the laboratory. Probably this 

 can be accounted for by the cooler nights and less abundant 

 food in nature, both of which would tend to decrease meta- 

 bolic processes and so increase the length of the larval life. 



