MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
563 
Having thus considered the means which are employed in the function of respira- 
tion in insects, the manner in which it is performed, the quantity of respiration under 
different circumstances, and its duration in different media, it remains only to notice 
the relation which these bear to the volume of the structures concerned in the dif- 
ferent states and species. 
We have seen that in the larva state the respiratory organs in most species are 
very small, and that it is only in the perfect condition that they acquire the maximum 
of development. But in the pupa, or intermediate state, these organs are much larger 
than in the larva, yet the insect requires a much smaller quantity of air for its sup- 
port in a given time. Hence it follows that although the organs concerned are of 
greater volume, the activity of respiration is diminished ; so that the pupa is enabled 
to endure the effects of noxious media, or the privation of air, much longer than the 
larva, and the larva, as in the case of many Hymenopterous insects, longer than the 
perfect individual. The larva of an insect is analogous to the child, or new-born off- 
spring of the mammiferous animal, and the analogy is the most perfect in its earlier 
condition. The pupa state bears a relation to the whole life of the insect similar to 
that which the hybernating condition bears to the life of the hybernating animal. In 
that state the volume and velocity of the circulation are diminished ; the temperature 
of the body (which I hope to have the honour hereafter of proving to the Society is 
always higher than the surrounding medium in insects in a state of activity,) is then 
scarcely, if at all, above that of the atmosphere, and the respiration, as we have seen, 
is almost entirely suspended. This is exactly the condition of the hybernating Mam- 
malia. When the insect awakes from its pupa state through the influence of external 
stimuli, its respiration, circulation, and temperature are all increased, and its capa- 
bility of supporting existence in noxious media is diminished. It is gradually deve- 
loped into the perfect animal, takes on itself the active duties of its existence, con- 
tinues its kind, and dies. But even during this its perfect condition it occasionally 
passes into the hybernating state, which I shall consider more particularly on a future 
occasion. 
Description of the Plates. 
PLATE XXXVI. 
Fig. l.'Part of a tracheal vessel of the larva of Papilio brassicce, Linn., exhibiting 
the spiral fibre ( a ) and the external or serous membrane ( b ). 
2. The respiratory organs contained within the abdomen of Bombus terrestris 
(Humble-Bee, magnified 10 diameters). 
(a) Two large brown tracheee, which pass through the petiole which 
connects the abdomen with the trunk, and are dilated in the first segment 
4 c 2 
