72 NATURAL HISTORY. [cH. III. 



and the gum dissolved, so that the insect has then 

 only to push against the end of the cocoon with its 

 head, in order to make its way out ; while others, 

 including Reaumur, consider that no fluid is em- 

 ployed, but that the head becomes a battering-ram, to 

 burst through the cocoon, breaking the threads in 

 its passage ; the facetted eyes being considered to 

 act as fine files, assisting in making the aperture. 

 Count Dandolo, in his work on the silkworm, how- 

 ever, observes that the end of the cocoon is wetted 

 for an hour, and sometimes even several hours, be- 

 fore the moth makes its way out. " Perhaps," say 

 Messrs. Kirby and Spence, " the two opinions may 

 be reconciled by supposing the silkworm first to 

 moisten, and then break the threads of the cocoon." 

 In other instances, in which more solid materials 

 than silk have been employed, such as grains of 

 earth, or chips of wood, the difficulty appears 

 greatly increased thus we have met with the co- 

 coon of the puss moth (Cerura vinula), in its natu- 

 ral situation upon the bark of willow trees, and it 

 has been with the greatest difficulty that we have 

 been able to cut it open with a penknife ; that this 

 was, however, owing to the hardness of the gummy 

 secretion with which the caterpillar (whose remark- 

 able form we have subsequently noticed) had ce- 

 mented the dust and chips of willow together, of 

 which the cocoon is composed, is evident, for had 

 it been formed only of silk and chips, it would have 

 readily yielded to the knife ; but the caterpillar, in 

 a state of confinement, will moreover build its case 

 with gnawed bits of paper, which, when dried, ac- 

 quire an equal consistence with the chip-cocoons. 

 Now the mouth of this moth is of a very rudi- 

 mentary nature, and from the perfect and smooth 

 appearance of the down upon the head of the 

 newly-disclosed moth, it is evident that some other 

 method than force must have been adopted to work 

 a passage through so hard a wall. We must there- 



