146 
MR. W. F. BARLOW’S OBSERVATIONS ON THE 
produced by mechanical irritation, especially by irritating the last segment of the 
abdomen. I cut off this segment, and then introduced a long pin, which I moved 
up and down cautiously, with the view of destroying the ganglia, taking care not to 
injure the abdominal walls. The respiratory movements ceased entirely, and were 
not renewed; it became impossible, also, to occasion reflex actions by irritating the 
abdomen. 
This experiment I have twice repeated with the same results. 
Injiuence of Temperature and Galvanism on the Respiratory Movements. 
The respirations of the dragon-fly present the same variations in vigour, as do the 
other movements, and the whole apparent life, according to the temperature of the 
medium in which it is placed. A kind of sleep overcomes the insect in the cold 
nights of autumn, after which it is found numb and motionless upon hedges, appear- 
ing as if dead, but easily revived by the sun’s heat, or by artificial warmth. At these 
times its breathing is probably often suspended for a long period; and were it not 
that (as the following among many experiments show) the movements can be re- 
newed after long suspension, the insect would be much more short-lived, and would 
perish at any considerable fall of temperature. 
Exp. XX. — I put a dragon-fly {Libellula depressa), which was breathing at the rate 
of about forty-five in the minute, into water of the temperature of 100° F. The respi- 
ratory movements increased to 110. On removing the insect, and exposing it to the 
air, they were reduced to fifty. On replacing it in water of the same heat, the respi- 
ration again became greatly accelerated, but very quickly ceased, and was not re- 
newed for a long time. 
Another dragon-fly, breathing at the rate of thirty-five, was put into water at 90°, 
and its respiratory movements were raised instantly to seventy. 
Exp. xxi. — I put a dragon-fly into a freezing mixture at 33°, and kept it in for 
thirty seconds. When taken out it was not respiring, but in less than a minute began 
to respire at the rate of thirty-five in the minute. I again immersed it for nearly three 
minutes. The respiratory movements this time ceased much longer and were more 
gradually renewed. The general activity of the insect was also more deeply affected. 
At first it seemed nearly insensible, and its voluntary movements were few and slug- 
gish ; but by degrees it became active. When it was breathing faintly and irregu- 
larly, in consequence of its exposure to the cold, I put it into water of the tempera- 
ture of 98°. The respirations rose to 108, but they were still feeble, and the insect 
showed considerable excitement. 
Exp. xxii. — -The temperature of the air being 70° F., I put a dragon-fly, which was 
breathing vigorously, into water at 34°. After two minutes I removed it, and all 
movement had entirely ceased ; but in a few minutes the respiratory movements were 
renewed, and it quickly recovered. I immersed it again with the same result. After- 
wards, having let it remain for half an hour, I galvanized it while it was perfectly 
