STATES OF INSECTS, (Pupa.) 261 
amongst the Hymenoptera, the Chalcidites (Ichneumones 
minutt L.); amongst the Lepidoptera, the subcutaneous 
tribes; and the majority of the Diptera,—remain as 
pupze only a few days or weeks: while the larger species 
in all these orders commonly exist in the same state se- 
veral months—many even upwards of ¢wo years. There 
are, however, numerous exceptions to this rule; for some 
large pupze are disclosed in a much shorter time than 
some others not a twentieth part of their bulk. 
The reasons both of the rule and of the exceptions to 
it are sufficiently obvious. And first, as to the rule :— 
If you open a pupa soon after its assumption of that state, 
you will find its interior filled with a milky fluid, in the 
midst of which the rudiments of its future limbs and or- 
gans, themselves almost as fluid, float. Now the end to 
be accomplished during the pupa’s existence is, the gra- 
dual evaporation of the watery parts of this fluid, and the 
development of the organs of the inclosed animal by the 
absorption and assimilation of the residuum. Reaumur, 
by inclosing a pupa in a stopped glass tube, collected a 
quantity of clear and apparently of pure water, equal to 
eight or ten large drops, which had evaporated from it, 
and was condensed against the sides of the tube, and it 
was found to have lost an eighteenth part of its weight+. 
It is plain, therefore, that this necessary transpiration, 
other circumstances being alike, must take place sooner 
in a small than in alarge pupa. Next, as to the excep- 
tions:— Since the more speedy or more tardy evaporation 
of fluids depends upon their exposure to a greater or 
less degree of heat, we might @ prior? conclude, that 
pupze exposed to a high temperature would sooner at- 
4 Reaum. i. 383. 
