THE TEMPERATURE OF INSECTS. 289 



be well explained by the prevention of evaporation from the 

 former. 



With regard to the effects of exercise, it was shown by New- 

 port 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. euphorbia 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 



