OF RESPIRATION. 399 



of the appetite likewise exercise great influence upon the function of 

 respiration, and indeed hunger, as in general, acts also enervatingly upon 

 respiration. Hungry insects breathe more slowly, but also longer, than 

 well-fed ones inclosed in the same quantity of air. The latter, how- 

 ever, produce, proportionately, considerably more carbonic acid. A 

 Cetonia, which was starved for three days, inspired less by half as 

 much air and rejected only one quarter as much carbonic acid as a 

 well-fed, healthy individual of the same species. The results are 

 similar in butterflies experimented upon under the same circumstances. 



That the developing egg respires precisely in the same manner, 

 and under the same conditions, as the subsequent perfect insect, has 

 been proved above by experiments in our description of the develop- 

 ment of eggs. 



234. 



Upon a careful investigation of respiration by means of gills, the 

 same results are produced ; the gills also imbibe oxygen, and give off 

 carbonic acid. But the question suggests itself whether in insects 

 which breathe by gills, these gills, as in the other animals with 

 universally distributed blood-vessels, imbibe merely oxygen and expire 

 carbonic acid, or whether they inspire perfect atmospheric air and 

 expire the remainder, containing carbonic acid and azote, having sepa- 

 rated the oxygen from it. We must first inquire, whence do the gills 

 derive their oxygen ? Do they decompose the water, consisting of 

 oxygen and hydrogen ? Or do they merely decompose the atmospheric 

 air contained within the water ? All experiments convince us that 

 the air only which is contained in the water is changed, and not the 

 water itself. Therefore, all animals die in distilled water deprived of 

 air, and, what is still more, insects die even in well water, which 

 contains more carbonic acid and in which less air is intermixed than in 

 the water of rivers or ponds. This prejudicial effect of well water 

 extends even to those insects which breathe through air tubes and 

 spiracles, and which for this purpose ascend to the surface of the water: 

 these also die quicker or slower in well water. But this does not 

 answer the question whether insects imbibe oxygen or air through the 

 gills. I think I must conclude that they extract the latter, from the 

 following considerations. 



In the first place, because the larvae which breathe through gills 

 exhibit the same internal apparatus as those which breathe through 

 spiracles, and indeed generally possess larger internal air tubes than 



