MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
549 
entirely obliterated. The quantity of air expired through the different orifices must 
therefore be greater at the anterior than at the posterior ones. But if one of the 
larger Humble-bees ( Bornbi ) be placed in water, and allowed to remain completely 
submerged until it has become nearly asphyxiated, the fact will then be still more 
apparent. At first there will be two large bubbles expired from the anterior spi- 
racles, on each side of the trunk, at each longitudinal contraction of the abdominal 
segments, which corresponds to each expiration ; but as the insect becomes more 
completely asphyxiated, the bubble of air will be only partially expelled from the spi- 
racle, and again withdrawn at the entrance, without having escaped, at each longi- 
tudinal extension of the segments, which corresponds to each inspiration, while not 
a single bubble of air can be detected at the entrance of the posterior abdominal seg- 
ments*. It is evident from this that it is chiefly through the anterior spiracles that 
respiration is performed ; and it may from hence be inferred that the manner in which 
the insect prepares itself for flight is exactly like that of birds under similar circum- 
stances. At the moment of elevating its elytra and expanding its wings the anterior 
pairs of spiracles are opened in the act of inspiration, and the air rushing into them 
passes into the tracheee of the whole body, distending the air-bags and rendering the 
insect of less specific gravity, so that when the spiracles are closed at the instant when 
the insect endeavours to raise itself in the air, it is enabled to sustain a long and 
powerful flight with but little expenditure of muscular power. This is the condition 
of respiration in the perfect insect. In the pupa, and still more so in the larva, re- 
spiration is performed more equally by all the spiracles of the body, and less parti- 
cularly by those of the thoracic segments. But even in these conditions of the insect 
the bubbles expired from the three anterior pairs of spiracles are the largest, and 
consequently these spiracles are the most important ones. It is thus evident that in 
the larva state the condition of respiration is but little advanced beyond that of the 
higher Vermes, and that it is only when the insect has passed through all its changes 
that its respiration is similar to that of the more perfect animals, which the insect 
then greatly resembles both in external and internal conformation. 
The quantity and rapidity, or activity, of respiration appear to bear some relation 
to the muscular power of the insect in a state of activity. All volant insects, and 
among these particularly the Hymenoptera , respire with a greater rapidity in a given 
space of time, and degree of atmospheric temperature, than terrestrial insects, and 
in their larva condition much less than in their perfect. In the common Hive-Bee, 
Apis mellifica, Linn., I have counted from one hundred and ten to one hundred and 
sixty contractions of the abdominal segments per minute when the insect has been 
* DeGeer appears to have made a similar observation, which he considered as expiration and inspiration, 
but the correctness of the opinion has been doubted by Carus, vol. ii. p. 167. Mr. Goadby has also noticed 
the contractions of the segments as analogous to acts of inspiration and expiration, but has not expressed an 
opinion respecting respiration being carried on chiefly through the anterior spiracles. See Medical Gazette. 
April 2, 1836. 
