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mer months. All of them, however, changed much 
more rapidly, from the permanent continuance of 
the heat, than if they had been exposed, even in 
summer, to the variable temperature of the open air. 
The insects, thus prematurely produced, were per- 
fect in all their parts, and the females laid their eggs 
as usual ; so that, by this method, butterflies maybe 
made capable of giving birth to two generations in 
the year, though in ordinary circumstances they af- 
ford but one. The same results were obtained by expe- 
riments made on the pupse of various other insects. 
547. M. de Reaumur, likewise, confined several 
pupse in a hollow sphere of glass, and placed them, 
with the eggs, under a brood-hen, leaving an aper- 
ture in the glass, by which fresh air could enter. 
The next day, the interior sides of the glass were 
covered with vapour that issued from the pupse, and 
had collected into small drops of water. These were 
removed, and did not appear afterwards, the greatest 
transpiration having occurred during the first day. At 
the end of four days, he saw, as he observes, the first 
butterfly that had, perhaps, ever been born under a 
hen, and the first of this species of pupa that had 
ever remained so short a time in that state ; for others 
of the same species, in the open air, require from 
twelve to sixteen days to complete the same series of 
changes *. 
- 54-8. On the other hand, by keeping the pupae of 
insects in a vault, where the temperature was only 
8 or 10 Reaum. above the freezing point, their e- 
* Mem. pour I'hist. des Insectes, torn. ii. p. 8. et seq. 
