276 
MR. NEWPORT ON THE TEMPERATURE OF INSECTS. 
place at certain periods in the capacity of the respiratory organs, which seem to be- 
come oppressed, and their full expansion prevented by the remarkable accumulations 
of fat which always exist in the bodies of insects before passing into the true hyber- 
nating condition. Thus before the larva assumes the condition of pupa it feeds most 
voraciously, and an immense quantity of fat is collected within it, and if it has been 
properly supplied with food, it acquires its utmost size and weight many hours be- 
fore it changes to a pupa. During the interval which elapses between its full deve- 
lopment as a larva and its change into the pupa state it is often much less active, and 
has the appearance of an animal suffering from repletion : it ceases to eat, it is more 
sluggish in its movements, often sleeps a great deal, and perspires copiously ; its 
average temperature is lower than it had been a day or two previously, and its quan- 
tity of respiration is also diminished. These appear to be conditions which induce 
the phenomena of its transformation, because I have repeatedly found that if a larva 
be deprived of its proper quantity of food, its change into the pupa state does not 
take place so early, but is retarded for two or three days. On the other hand if the 
insect be supplied to repletion, its change will be slightly hastened. Thus if several 
specimens of the larva of the Sphinx be hatched at about the same time but supplied 
with different kinds of food, those which are fed upon one kind of plant will often 
arrive at maturity and undergo their changes before those which are fed upon another. 
In these cases it is inferred that a plethoric condition, which is supposed always to 
precede the change to the pupa state, occasioned by the accumulated fat within the 
body compressing the respiratory organs, and thereby preventing the full aeration of 
the circulatory fluids, is induced in the one instance earlier than in the other, owing 
to the more nutritious quality of the food supplied to the insect during the first few 
days after it has left the egg*. There is also another strong reason for believing that 
this condition of body is closely connected with the phenomena of transformation, in 
the circumstance that, although for many hours immediately preceding the change, 
the quantity of respiration, relatively to the size of the insect, becomes diminished, yet 
within one hour of the actual period of rupturing and throwing off its skin, the insect 
makes several very powerful and laboured inspirations ; and it is then probably that 
those tracheae which seem to have become compressed and diminished in calibre 
during the plethoric state, begin again to be distended, previously to their subse- 
quent development into the large respiratory sacs of the perfect insect. This enlarge- 
ment of the sacs is slowly progressive during the earlier, but most rapidly so during 
the latter period of the pupa state, while particularly in the Sphinx, it is almost sus- 
pended in the middle, or intervening period of this state, the period when the insect 
is in its most complete state of hybernation. The enlargement, as suggested on a 
former occasion*, seems to keep pace with the gradually diminishing size of the 
alimentary canal, and with the absorption of the accumulated fat, and since it is well 
known that a higher or lower degree of atmospheric temperature will either accele- 
rate or retard the completion of these changes in the pupa, it may not be unreason- 
* Philosophical Transactions, 1836, Part II. p. 534. 
