MODES OF CHANGE INTO VUPM. 77 



enclosed in a thin web, without a brace, similar to that 

 of the spotted skipper, is uncertain. Should the figures 

 of Lewin be correct, it follows that such unbraced pupae 

 will present us with a. fourth variation among the butter- 

 flies; and this will be analogous to the pupse of the 

 spinning moths, or silkworms (^Botnbycides^, subse- 

 quently noticed. 



(68.) But the typical forms of perfect Pupce are 

 not all to be found among the butterflies ; and this shows 

 us, by the way, that a system built upon this stage of 

 an insect is not a whit more valuable than another which 

 rests solely upon the caterpillar. Hitherto we have 

 seen that these creatures perform their transformations 

 in the same element as that in which they were born ; 

 but on entering among the crepuscular or twilight 

 flying tribe (^Sphingides Sw.), we find that the larvje 

 quit the air and hide themselves in the bowels of the 

 earth, as if they " loved darkness better than light, be- 

 cause their type was evil." At the head of this tribe 

 stands the death's-head moth (^Sphinx Atropos), car- 

 rying upon him the " sign and seal" of the symbol 

 which Nature has designed him to be. Upon the thorax 

 of this extraordinary insect, which is the largest moth 

 found in Europe, the figure of a human skull, the em- 

 blem of death and of the grave, is so distinctly stamped, 

 that a casual observer might easily imagine it was the 

 work of some cunning limner desirous to give an un- 

 natural terror to the aspect of a really harmless insect. 

 Now, the caterpillar of this forbidding creature, when 

 it is about to undergo its transformation, penetrates to 

 more than a foot deep into the earth; and all the true 

 sphinges do the same ; but Nature does not pass to 

 these subterranean pupse without many gradual modi- 

 fications. Some of the hawk moths spin themselves a 

 web on the surface of the ground, which is covered by 

 leaves : others proceed a step further, and make use of 

 particles of dirt in preference : next come a few who 

 repose themselves in a little hollow grave, so that they 

 hardly lie beneath the surface : succeeding species dig 



