THE PUPA. 333 



segments of the caterpillar, showing that the pupa is being 

 withdrawn from that part. The pupa is pushed forward 

 by a vigorous use of the cremaster. In this manner the 

 skin on the posterior segments is pushed back, and the 

 pressure on the anterior segments becomes so great as to 

 nearly bend under that part of the body. The insect takes 

 short rests at intervals during this process. Next, the skin 

 on the fourth segment splits along the dorsal line, the split 

 continuing forward and backward, and in a few seconds 

 extends from the base of the head to the annulation between 

 the fourth and fifth segments, the pupa, in the mean time, 

 forcing itself outward against the opening thus made. In a 

 few seconds more the movements of the pupa, aided by the 

 pressure from behind, which it is able to exert by means 

 of its cremaster, splits the head down on each side of the 

 clypeus to the mouth parts, and the pupa emerges by pass- 

 ing outward through the opening, the whole process taking 

 about fifteen minutes. 



The newly formed pupa is very soft and of a light color, 

 with the remains of the larval tubercles and markings 

 plainly visible, but these disappear and the pupa grows 

 harder and darker when exposed to the air. Caterpillars, 

 in their attempts to pupate, sometimes burst the thin pupal 

 skin and die from the escape of the fluids from the body. 

 In changing from the larval to the pupal stage, the insect 

 loses about thirty-five per cent, in size and nearly forty-five 

 per cent, in weight. A small part of the weight is left in 

 the larval skin and silk. How the insect, as a rule, fastens 

 itself to the silk in which it is enclosed, is not fully known. 

 In one case, however, a pupa was seen to emerge and fall 

 into the network of silk, when, by a wriggling motion, it 

 picked up the silk threads on its cremaster and then hung, 

 from gravity, head downward. 



The maximum time spent in the pupal stage by one 

 hundred females was found to be 14 days, the minimum 7 

 and the average 10.65. The maximum time spent in the 

 pupal stage by eighty-eight males was found to be 17 days, 

 the minimum 9 and the average 13.41 days. 



Pupa (Plate I, Fig. 5, and Plate 48). The pupse of the 

 males vary in length from three-fifths to four-fifths of an inch, 



