The Metamorphoses of Insects. 59 



The hard chitinous integument which envelops the pupa is 

 not the larval skin ; it is formed by the hardening of a sticky- 

 fluid thrown off at the moment when the caterpillar skin is also 

 thrown off. If a mature caterpillar be dissected just before this 

 period, the various organs of the pupa, wings, limbs, etc., can be 

 seen to be perfectly free-. After a longer or shorter period of 

 rest the perfect insect breaks through the cuticle of the pupa, 

 and escapes. 



On reviewing the life-history of this moth it will be observed 

 that a great difference in the way of life accompanies the more 

 complicated metamorphosis. In the cockroach, the young 

 leads practically the same kind of life as the adult. The 

 difference between them is hardly more than that the earlier 

 stages are devoted to growth, the latest to reproduction. This 

 difference in way of life is also seen between the caterpillar and 

 the moth — in a more marked fashion, indeed, for the feeding 

 of a perfect insect is often practically nothing at all; but, 

 whereas the caterpillar eats leaves, the moth sucks the juices 

 of flowers, and has, as a consequence, a totally different 

 arrangement of the mouth organs. It is this diversity of mode 

 of life which has led — in the opinion of some — to not only the 

 extraordinary difference between larva and imago, but also to 

 the existence of the quiescent pupa. To change the biting 

 parts of the caterpillar's mouth for the sucking proboscis of 

 the moth would necessitate, if the development were gradual, a 

 series of intermediate stages, which would not be serviceable in 

 either capacity. Hence, during a quiescent period, in which no 

 food is taken, and during which the animal is protected by the 

 silk cocoon, the changes could be, and are, brought about. 



The Blow-fly {Musca vomiioria) has a series of metamorphoses, 

 which do not differ greatly from those of the silk-worm. From 

 the egg is produced a larva, which differs from that of the silk- 

 worm in being apodous ; the limbs are absent. The pupa, 

 into which the maggot turns, is again different, in that its outer 

 brown chitinous case is not a new formation, but the shrunken 

 skin of the larva. Within this skin the process of breaking 

 down of the tissues goes on rapidly. The generative organs, 

 however, appear to be continuous with those of the larva, where 



