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TEXT-BOOK OF ENTOMOLOGY 



delicate, purplish, powdery layer left in the cast shells of the pupae 

 of saturnians, Catocalae, and other moths, might possibly be such a 

 pellicle, but this view has been dispelled by the following statement 

 of Professor Bngnion in a letter answering an inquiry whether he 

 had noticed such a pellicle. 



"A liquid which is secreted in a few minutes at the time of the last moult, 

 forms in drying a yellowish layer spotted with black (in Pieris brassicce). This 

 layer extends around the entire pupa, and serves both to protect it and to glue 

 together the wings, legs, etc., in their new position. The dried liquid on the 

 surface of the pupa, and by means of which the appendages are glued to the 

 surface, very likely corresponds to the pellicle of which you speak." The newly 

 exposed integument is at first pale and colorless, but soon assumes the hues 



hy- 



FIG. 566. Transverse section through the prnthnracic segment (ventral face) of larva of Pieris 

 Itrttxxica 1 . about 12 hours before pupation : c, euticula : /. hy, large glandular ^?) hypodermal cells; 

 gradually passing into normal hypodermal cells (hy). Gonin del. 



peculiar to the species, and the insect, at first exhausted, after a short rest 

 becomes active. 



E. Howgate has noticed under the microscope peculiar internal movements 

 in a small immature transparent geometrid while moulting. " Each separate 

 segment," he says, " commencing at the head, elongated within the outer skin, 

 whilst the next ones remained in their former state. Each segment in its turn 

 behaved in this curious manner until the last was reached, when the motion 

 was reversed and proceeded toward the head, when it was again reversed. . . . 

 The whole proceeding appeared as if the larva was gliding within itself, segment 

 after segment, the outer skin remaining as if held by the other segments, whilst 

 the particular one in motion freed itself within. After remaining motionless 

 for a short, interval, the skin near the head swelled and burst open at the back. 

 . . . Presently out comes the head of the new caterpillar, pushing forward the 

 old one. . . . After a short struggle the new true legs appear, pushing off and 

 treading under foot the old ones. Then by violent wriggling movements the 

 abdominal legs were extricated. Then all is clear, and the larva, which is quite 

 exhausted, coils itself up and literally pants for breath." (The Naturalist, 

 November, 1885, No. 124, p. .T.C, quoted in Psyche, iv, p. .'527, 1S87.) 



Since the worms and most other arnetabolous invertebrates are not known to 

 moult their integument, the body steadily increasing in size without frequent 



