INSECTS IN GENERAL. 7^ 



behind, advances on the opposite point, where the head is. 

 In the larvae of ephemerae, in those of phryganae, gnats, &c., 

 genuine gills appear to exist, which are always in motion 

 when the animal respires. This is a kind of anomaly in 

 insects, which merits particular attention, especially in the 

 ephemera, if, as Swammerdam has imagined, these insects 

 have the power of fecundating the eggs, after they are sepa- 

 rated from the body of the mother ; this, as we have already 

 seen, constitutes a marked analogy between the fish and some 

 batracian reptiles. 



From these anatomical researches, it follows, that as the 

 insects have neither heart nor vessels, it is not the blood which 

 proceeds to seek the air, but the air which visits every part 

 where the fluids exist ; the result however is the same, 

 and the two functions are performed, just as two numbers 

 may be multiplied indifferently by each other, and will pro- 

 duce the same quotient. 



It has been proved that oxygen is necessary to the respi- 

 ration of insects ; that this gas is absorbed, that the carbonic 

 acid is disengaged, and that the matter of caloric is deve- 

 loped in this animal operation. 



Though it seems probable that the temperature of insects 

 may be pretty nearly the same as that of the atmosphere, 

 yet it must be confessed that we are not positively acquainted 

 with this temperature, for two reasons, first, because it is 

 very difficult to observe and estimate it, and secondly, be- 

 cause the body of the insect is soon placed in equilibrium with 

 the matters which surround it; nevertheless, it has been 

 observed, that insects which live in a social state, and more 

 particularly, in our climates, ants and bees, when they are 

 assembled, develope a temperature almost equal to, if not 

 higher than that of man. A thermometer, placed in winter 

 in the centre of a hive, remains there, constantly elevated 

 from 28? to 30° of Reaumur, and when these insects are 



