55 



functions, the power of generating heat, and the influence 

 of activity of the vital functions on the increase of this 

 power, are shewn, in a table drawn up to illustrate a period 

 of 47 hours of the life of one of these insects. At the commence- 

 ment of this period the animal weighed 79'8 grains, at the 

 termination of it it had gained 1485 grains, in the whole 

 period it had eaten 79*95 grains of food. It had passed 

 29-8 grains of foeces, and had therefore lost 35-3 grains by 

 transpiration and respiration. During this period the 

 temperature of the insect was always above that of the 

 external air, and the minimum difference being 0°.4, the 

 maximum difference being 1°.2, the medium being about 

 0.8 of a degree. This, taken along with the great loss 

 by transpiration, indicates a very considerable power of 

 generating heat. The excess of the temperature of the 

 animal above that of the air was greatest when it was most 

 active, although the gaseous expenditure was increased at 

 the same time, and least when it was asleep. 



From what precedes, it may be inferred that animals are 

 divided into two great classes with regard to their tempera- 

 ture. The first to which the epithet of warm-blooded is 

 applied is, that in which the individuals have a power of 

 preserving their heat at a mean considerably above that of 

 the mean heat of the atmosphere, from which mean, under 

 any circumstances in health, they do not deviate by any 

 considerable amount ; that this amount of deviation, how- 

 ever, varies in different animals, at different ages, in different 

 climates, and in different seasons, — the greatest amount 

 being in the feeblest animals at the earliest and latest ages, 

 in the warmest climates, and in the summer season. The 

 second class to which the epithet of cold-blooded has been 

 applied is, that in winch the individuals have, in ordinary 

 temperatures, a comparative slight power of maintaining 

 their temperature above that of the external medium ; and 

 their heat, as measured by the thermometer, must, therefore, 



