142 
MR. W. F. BARLOW’S OBSERVATIONS ON THE 
in rate. The head was removed, and they became 29,20, 14, 11, 11, 14, and were 
considerably reduced in force. In another insect they were reduced from 56, 37, 46, 
40, 37, 36, to 20, 14, 12, 1 1, 9, 6. 
Exp. vii. — I counted the respirations of a dragon-fly eleven times, in as many 
minutes, with intervals of a quarter of a minute between each two. They were 100, 
101, 98, 100, 110, 106, 108, 108, 108, 108, 106. I then removed the head, and num- 
bered the respirations in the same manner again, and found them 55, 61, 70, 70? 66, 
70, 68, 67, 70, 70, 62. 
The evidence of all the foregoing observations, proving the diminution, in both rate 
and force, of the respiratory movements when the head is removed, may serve to 
illustrate the admitted correspondence of the supra-oesophageal and sub-oesophageal 
ganglia of the insect, with the brain and medulla oblongata of the vertebrate animal. 
But that these movements should be only diminished, and should not cease, as they 
do when, in a vertebrate animal, the medulla oblongata is destroyed, — this may be 
regarded as indicating that there is, in the insect, a multiplication and diffusion of 
the nervous centres for the respiratory movements, corresponding with the plan of 
multiplicity in the respiratory organs. The same conclusion may be derived from 
experiments, which will be related, of the effects of dividing the body into segments. 
Injluence of Shock on the Respiratory Movements. 
Exp. viii. May 11, 1848. — Wishing to ascertain the effects of shock upon the 
respiratory movements, I took a dragon-fly {Libellida depressa) which had been 
caught the day before, and was breathing pretty vigorously, between forty and forty- 
five times in the minute, and crushed its head completely and suddenly. There fol- 
lowed perfect stillness ; the respiratory movements were quite indiscernible, until 
between three and four minutes had passed; then, they could be just seen; but they 
soon ceased again. After about four minutes more had elapsed, the respiratory 
movements were marked with rather more power, and persisted ; but they were as 
yet very faint and unequal. In two hours, though they continued, they were still 
without vigour ; and so they remained twenty-four hours later. 
Exp. ix. May 13, 1848. Temperature 64°. — I took a dragon-fly, which was 
breathing at the rate of thirty-six, and crushed the head and upper part of the thorax. 
The respiratory movements ceased, but in less than a minute were resumed; they 
were, however, very feeble and so remained. In about eight minutes from the 
infliction of the shock, the movements were at the rate of thirty-nine, but their power 
was exceedingly diminished, and they required minute watching to observe them 
properly. 
Exp. X. — I crushed the head and thorax of a dragon-fly; the respiratory move- 
ments ceased for two minutes. At the same time, another, while in full activity, was 
struck a sharp blow which inflicted a like injury. The respiratory movements 
stopped instantly, were suspended for many minutes, and never recovered any degree 
of power. 
