350 
[Assembly 
Its characters .—The flax seed shell has now become quite brittle, 
breaking asunder transversely if rudely handled, and one of its ends 
slipping off from the inclosed pupa like a thimble from the end of 
the finger. On removing the pupa (fig. /.) from its case, it is found 
to be 0.13 long by 0.05 broad, of an oval form, with rounded ends, 
and having its limbs and body enveloped in separate membranes. 
The thoracic portion is slightly narrower than the abdominal. The 
wings do not quite attain the middle of the length of the body. 
The outer pair of feet come out from under the tips of the wings, 
and reach to the anterior margin of the penultimate abdominal seg¬ 
ment, slightly curving inwards at their tips. The next pair of feet 
are somewhat shorter, and the inner pair are shorter still. They all 
lie in contact with each other, and in a direction parallel with the 
body. The abdominal segments are distinctly marked by strongly 
impressed transverse lines, and are of a milk-white color, the thorax 
and head being of a delicate pale pink-red, and the feet translucent- 
white. On the anterior margin is a chestnut-brown crescentiform 
mark. It will hence be perceived, that in all the details of its form, 
the pupa of the Hessian fly coincides precisely with those of the 
other species of this genus which have been described. 
Its change into a fly .—The time for its final transformation hav¬ 
ing arrived, the pupa breaks open and crawls from its puparium or 
flax seed case, and works its way upwards within the sheath of the 
leaf, until it arrives at some cleft in the now dead, brittle and elas¬ 
tic straw ; through this cleft it gradually, by bending from side to 
side, crowds its body until all except the tip of the abdomen is pro¬ 
truded into the air, the elasticity of the straw causing it to close to¬ 
gether upon the tip of thfi abdomen, so much as to hold the pupa in 
this situation, secure from falling to the ground ; and as if to pre¬ 
serve the body in a horizontal position, the feel are slightly separa¬ 
ted from the abdomen, and directed obliquely downwards, with their 
tips pressed against the side of the straw, thus curiously serving, 
like the brace to the arms of a sign post, to support the body from 
inclining downwards. Thus securely fixed, and now freely exposed 
to the drying influence of the atmosphere, the outer membrane of 
the pupa speedily exhales its moisture, and as it becomes dried, 
cracks apart upon the back part of the thorax ; out of this clgft the 
inclosed fly protrudes its head and thorax more and more, as it gra- 
