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V. Observations on the Respiratory Movements of Insects. By the late William 
Frederick Barlow, F.R.C.S. Arranged and communicated by James Paget, 
F.R.S. 
Received August 20, — Read November 16, 1854. 
The following essay contains the greater part of a series of observations, made 
between 1845 and 1850 , by one whose recent death deprived physiology of one of its 
most earnest truth-loving students. The papers, as left by their author, and com- 
mitted to me by his father, contained little more than a record of the observations. 
I have arranged them to illustrate certain general facts, and have added some of the 
conclusions which they plainly indicate. I have felt the more justified in making 
these additions, by the belief that my intimate friendship with Mr. Barlow would 
enable me to write what he would have written, had his life been spared. And in 
communicating his researches to the Royal Society, I believe I am fulfilling the design 
with which, not long before his death, he was preparing them for publication. — J. P. 
Natural respiratory movements of the Dragon-fly (Libellula). 
From nearly all the following observations it may be gathered that these move- 
ments constantly vary, in both rate and force. Volition and emotions, changes of 
temperature and of light, account for many of these differences ; and it might have 
been inferred that, on these disturbing causes being removed, there would be a great 
uniformity in the mode of breathing, if care were taken that observations should be 
made with strict regard to sameness of circumstances. It is not so, however- 
the respiratory movements become much more equal, but they are very far from 
maintaining true equality of rate and force, even within a short given period. They 
have times of acceleration and of decrease, which it is hard to account for. Within 
three or four minutes, even, their speed and strength will vary, although the insect 
be kept in unbroken quiet. And if different individuals be compared, it does not 
appear that the vigour of each insect, or the probable length of its life, can be cal- 
culated by the force of the respiratory movements. 
One of many similar observations may illustrate these statements. 
Experiment i. May 19 , 1848 . — I watched a dragon-fly {Libellula depressa) which 
had been caught the day before. Just before its capture it was pursuing its prey, 
and flying very swiftly, in all directions, in the sunshine. The temperature was 
moderate, and there was a slight breeze stirring. The respiratory movements corre- 
sponded with the activity of the insect, and were very quick and vigorous. I placed 
it under a glass, and noted its state on the following morning. The insect had 
