396 PHYSIOLOGY. 



breathe like all others, or rather like the majority of the larvae of the 

 Diplera. The second instance, however, is found in the Ichneumons, 

 which do not live in the intestine, but in the cavity of the body of other 

 insects, between the intestine and the skin. That these creatures must 

 breathe admits of no doubt ; and indeed that they breathe precisely in 

 the same way as the larvae of the other Hymenoptera, namely, through 

 spiracles, is as certain as that they do not at all differ in their organi- 

 sation from those larvee. We can, therefore, adopt no other supposition 

 than that such larvae participate in the respiration of the insect upon 

 which they are parasitic, and that they breathe the air that passes 

 through the tracheae into the cavity of the body, or that they pierce a 

 trachea, and, remaining in its vicinity, respire the air pouring from it. 

 Such a wound to the respiratory apparatus would not produce death, 

 for it has still sufficient unwounded tracheae, and it would require only 

 to be a small branch that would admit of the passage of sufficient air for 

 the minute larva of an Ichneumon. Those caterpillars infested by 

 parasites are always evidently ill, and this disease may proceed perhaps 

 from the interruption in various parts of the function of respiration, 

 and this interruption, together with the constant decrease of the fatty 

 substance of the pupa, may deprive it of its remaining strength, and 

 thus slowly kill it. After the death of the pupa, the remainder of its 

 internal organs are consumed by the parasite, or else the numerous 

 parasitic larvse pierce the skin of the caterpillar, and thus kill it before 

 it can change into the pupa state. 



233. 



Having now shown the various kinds of mechanism by which 

 atmospheric air is admitted to the internal organs of respiration, we 

 further ask what is the object of this admission of atmospheric air, and 

 what changes does it itself undergo? The reply is given in the result 

 of the various experiments of Sorg, Hausmann, and others, upon the 

 decomposition of air during the breathing of insects, and it is, " All 

 breathing insects deprive the air of a considerable portion of its oxygen, 

 and give off in lieu of it carbonic acid." The quantity of oxygen 

 withdrawn by breathing varies according to the size of the creature, 

 and the intensity of its respiration, and the quantity of carbonic acid 

 given off varies just as much. But thus much appears confirmed, that 

 considerably more oxygen is consumed by the creature than carbonic 



