THE NATURE OF METAMORPHOSIS. 63 
become detached, and are gradually developed backwards, and 
encroach upon the anterior portion of the second segment. This, 
in accordance with the laws of development as established by 
Geoffroy St. Hilaire, that in proportion as one part of an organised 
body is increased beyond its ordinary size, the part or parts in its 
immediate vicinity are in a corresponding degree arrested in their 
development, becomes so much reduced, that in the nymph the 
second segment, which in the larva is of the same size as the third 
and succeeding ones, has not half its original extent, and being still 
further reduced in that state, constitutes at length the atrophied 
and almost obliterated prothorax of the perfect insect. But while 
the second segment is thus encroached upon by the first, it is in 
like manner encroached upon from behind by the third—the 
immense mesothorax, which supports the chief organs of flight in 
the perfect insect. The fourth segment, from the same cause, is 
developed backwards ; and the fifth, diminished to a very small 
size, exists only, as in the Sphinx, as the petiole which connects the 
thorax with the abdomen, thus leaving the nine posterior segments 
of the larva to the latter region, as stated when alluding more 
particularly to the number of segments in hymenopterous larve. 
The necessity for this additional sezment in the abdomen of these 
larve is a matter of much interest, and appears to be connected 
with the development of an apparently additional organ in the 
females of this class. 
“We have seen that after leaving the larva, or feeding condi- 
tion, the insect assumes one of a very different form, which is called 
the pupa, nymph, aurelia, or chrysalis state. . The two latter terms 
were applied by the older entomologists to this stage of transfor- 
mation in butterflies and moths. The term ‘aurelia’ was used as 
expressive of the beautiful golden colours or spots with which many 
species are adorned, as Vanessa urtice, Vanessa Atalanta, and 
others. The term ‘chrysalis’ had a similar signification. Linnzus, 
desirous of employing a term that would be applicable to this stage 
of transformation in all insects, adopted that of ‘pupa,’ because in 
a large majority of the class the insect is as it were swathed or 
bound up, just as children were formerly swathed. The kind of 
pupa, in which the future limbs are seen on the outside of the 
case, is called ‘obtected.’ Such chrysalides are represented in 
