THE PUPA AND IMAGO. 
85 
cases are developed, two on each. side. Slight altera- 
tions of colour and form are noticed, the antennm 
rapidly increase in length, and usually spots are seen 
on the occiput which show the seat of the future ocelli. 
The insect feeds as usual, but after a while it fixes 
itself permanently by its claws, and continues quies- 
cent for some hours. A rent then commences behind 
the eyes, which proceeds down the thorax, through 
which rent the brown head of the imago emerges. 
The antennae and legs are slowly pushed forward 
from the exuviae or sheath, which slips down the soft 
body of the fly by a kind of peristaltic motion very 
interesting to watch under the microscope. The skin 
is not inverted, but stands entire, even to the last joints 
of the antennae and the tips of the claws— the ghost 
of its former self These empty cases may be found 
by hundreds in the haunts of the rose Aphis. ^ 
THE IMAGO. 
When these winged forms first disengage themselves 
from their chrysalides, they are very pale in colour, and 
transparent. The wings, at first soft and pulpy, like 
wet vellum, grow very rapidly ; so much so that con- 
siderable difficulty is experienced in following with the 
pencil their outline under the camera. The wings do 
not unfold themselves, neither do they expand by an 
inflation of the chief nervures through an introduction 
of air from the tracheal system. They grow, indeed, 
in a regular manner, throughout all their parts, and get 
their full development in the short space of about 
twenty minutes. This feat of emergence of the imago 
appears to be almost a mechanical impossibility. It 
presents one of the most interesting and curious exhibi- 
tions of the microscope.! 
The moultings of the larvse, which often are very 
* Vide PI. II, figs. 1—3 ; PL XIY, fig. 3 ; PI. XXII bis, fig. 2. 
t Sir John Lubbock in bis ‘Metamorphoses of Insects’ interestingly 
