MOULTING OF CATERPILLARS. 169 



the fat which lies between it and the outer skin 

 seems to be absorbed into the bod t of the cater- 

 pillar, and of course swelling it out; while its abstrac- 

 tion from the interior of the outer skin renders this 

 much more dry, separates it from the inner skin, and 

 disposes it to harden and shrivel. 



The absorption of the fat also produces the re- 

 markable consequence of gorging all the channels of 

 nutrition, so that there is no longer any demand 

 upon the stomach for fresh supplies of food; and 

 hunger (which we imagine is caused either by the 

 want of the accustomed pressure of food on the 

 terminal nerves in the stomach, or of the irritation of 

 the absorbents when they are left empty) is no 

 longer felt. The caterpillar accordingly ceases to 

 eat, and having no incentive to action remains motion- 

 less. The outer skin, in the meanwhile, being 

 deprived of its internal moisture by the absorption of 

 the fat, goes on to harden and shrink, while all the 

 internal organs become enlarged by the nutritive fat. 

 The expansion, therefore, of the body of the cater- 

 pillar on the one hand, and the shrinking of the old 

 skin on the other, produce a mutual struggle, which, 

 from the continued operation of the causes, must, it 

 is obvious, be soon brought to a termination. 



The skin, from losing its internal moisture, loses 

 also a portion of its colour, and becomes obscure 

 and dull; and the caterpillar, from being girt and 

 squeezed by its pressure, begins to turn and twist 

 itself in various directions, to rid itself if possible of 

 the inconvenience. By continuing these movements, 

 the creature succeeds at length in rending the old 

 skin at its weakest part, which is usually on the 

 back, just behind the head; and in a few minutes, 

 using its body as a wedge, it may be seen issuing 

 through the breach.* The old skin is thus abandoned 



* Reaumur, Mem. i, 135. 

 VOL. vi. 15 



