THE ORGANS OF CIRCULATION AND RESPIRATION. 165 



Respiratory Activity of Insects. 



The respiratory activity of Insects varies greatly. Warmth, 

 feeding, and movement are found to increase the frequency 

 of their respirations, and also the quantity of carbonic acid 

 exhaled. In Liebe's* experiments a Carabus produced "24 mgr. 

 of carbonic acid per hour in September, but only '09 mgr. per 

 hour in December. A rise of temperature raised the product 

 temporarily to twice its previous amount ; but when the same 

 insect was kept under experiment for several days without food, 

 the amount fell in spite of its increased warmth. Treviranusf 

 gives the carbonic acid exhaled by a Humble-bee as varying 

 from 22 to 174, according as the temperature varied from 

 56 to 74 F. 



Larvae often breathe little, especially such as lie buried in 

 wood, earth, or the bodies of other animals. The respiration of 

 pupae is also sluggish, and not a few are buried beneath the 

 ground or shrouded in a dense cocoon or pupa-case. Muscular 

 activity originates the chief demand for oxygen, and accordingly 

 Insects of powerful flight are most energetic in respiration. 



A rise of temperature proportionate to respiratory activity 

 has been observed in many insects. Newport .J tells us how the 

 female Humble-bee places herself on the cells of pupae ready 

 to emerge, and accelerates her inspirations to 120 or 130 per 

 minute. During these observations he found in some instances 

 that the temperature of a single Bee was more than 20 above 

 that of the outer air. 



Some Insects can remain long without breathing. They 

 survive for many hours when placed in an exhausted receiver, 

 or in certain irrespirable gases. Cockroaches in carbonic acid 

 speedily become insensible, but after twelve hours' exposure to 

 the pure gas they revive, and appear none the worse. 

 H. Muller says that an Insect, placed in a small, confined 

 space, absorbs all the oxygen. In Sir Humphry Davy's 

 "Consolations in Travel "|| is a description of the Lago dei 



* Ueb. d. Respiration der Tracheaten. Chemnitz (1872). 



t See table in Burmeister's " Manual," Eng. trans, p. 398. 



J Art. " Insecta," Cyc. Anat. and Phys., p. 989. 



Pogg. Ann, 1872, Hft. 3. 



|| "Works, Vol. IX., p. 287. This passage has been cited by Rathke. 



