RESPIRATORY MOVEMENTS OF INSECTS. 
143 
Exp. xi. May 22. — To another dragon-fly whose respiratory movements were 
similarly feeble, after recovering from the shock of crushing the head, I applied 
stimulus by holding it over water of the temperature of 185°Fahr., and the strength 
and frequency of the movements were greatly increased. 
Exp. xii. — In a dragon-fly, which had been decapitated and was breathing distinctly 
at the rate of sixty- three, I crushed the last two abdominal segments. For a minute 
and a half the respiratory movements were but dimly visible; then they revived 
gradually. This shows the retrograde influence of shock. 
These experiments, while they confirm those which illustrate the influence of mere 
decapitation, prove also that the influence of shock, i. e. of sudden violent destruction 
of a part, is essentially the same in the insect as in the vertebrate animal. They 
show that the separation and evident distinctness of nervous centres do not so 
dissociate the parts, with which they are severally connected, as to place any of them 
beyond the influence of the injuries inflicted on the rest. And yet, while these effects 
of shock may prove the mutual relations of the several ganglia, the following experi- 
ments on the division of the body into segments may show how each ganglion is the 
centre for the respiratory movements of its own segments. 
Respiration in the separate segments of the Insect. 
Exp. xiii. Sept. 7, 1845. — I decapitated a dragon-fly, which was breathing vigor- 
ously at the rate of fifty-five in a minute. In five minutes the respiratory move- 
ments were forty-two, and considerably less forcible than before the decapitation. 
Eight minutes later they were thirty-nine. I now divided the abdomen of the insect 
into three segments, with care to produce as little shock as possible. At first I could 
discern respiratory contractions in that division alone which was attached to the 
thorax, and I waited as long as seven minutes before I could distinguish them in the 
remaining segments ; and now, in all, they were very weak in comparison with those 
in the thorax, and still more so in comparison with what had been noted in the per- 
fect insect. Had this been owing to shock, they would probably have been restored ; 
but twenty minutes later they were still indistinct, and at times imperceptible. The 
superior division continued to respire by far the most strongly. On placing the 
middle segment in my hand, the movements became, in about a minute, very distinct, 
and increased to the rate of 100 in the minute; but, on replacing it on the table, 
they became again obscure, and soon imperceptible. Three hours after the opera- 
tion no respiratory movements were observable, nor could any be excited, though 
the legs of the insect could be excited to retraction. 
Exp. xiv. Oct. 14, 1845. — I took a small dragon-fly, which was breathing power- 
fully at the rate of 116 per minute, the movements being possibly quickened by 
emotion. On removing the head, they were diminished, in one minute, to fifty-eight 
(just half the former frequency), and were much weaker. I divided the abdomen 
into two equal parts. The respiratory actions ceased awhile ; but the effects of the 
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