Page:The Zoologist, 4th series, vol 6 (1902).djvu/343

Rh be well explained by the prevention of evaporation from the former.

With regard to the effects of exercise, it was shown by Newport that the temperature of an insect at rest is always lower than when it is in motion; while Lecoq found that a species of Sphinx, during active motion, reached the normal temperature of birds, which is peculiarly high. Bachmetjew has considered the influence of exercise at ordinary room temperatures, at heightened temperatures, and under the application of cold. He found that at ordinary room temperatures (18·5°) Sphinx pinastri raised its temperature by rapid wing-vibration up to 36°. At this point the vibration ceased, owing to a partial paralysis of the wing-muscles; the temperature then dropped, and the paralysis passed away. On repeating the rapid vibration immediately paralysis set in again more rapidly, but not until the temperature reached 36°; furthermore, if the surrounding temperature was increased, less humming is required to bring on partial paralysis. There is therefore considerable ground for assuming that it is the heightened temperature which causes the partial paralysis. Just as there is a maximum temperature which brings on paralysis, so there is a minimum; thus D. euphorbiæ ceased rapid vibration when its temperature was at 17·6°, and all movement stopped at 0·5°. Putting these observations together, we see that for the Sphingids observed normal flight is only possible roughly between the temperatures of 18° and 36° C.

The influence of food and of respiration is only touched upon, but we may gather that everything that tends to increase metabolism tends also to raise the temperature.

In the second part of the volume the vital temperature extremes of Lepidoptera are discussed, especial attention being paid to the minimal temperature; and at the outset a very curious phenomenon is offered for consideration. If a butterfly or moth be cooled by being kept in an iced chamber, a certain point of under-cooling is reached (called the critical point, or K); at this point the temperature suddenly rises through more or fewer degrees, and freezing takes place at a temperature above the critical point (called the normal freezing-point, or N). This behaviour of the juices of insects shows a striking analogy to the under-cooling of water under certain conditions. This process