OP INSECTS. 155 



was a secreting organ, although he did not determine 

 the nature of the alleged secretion. Other opinions 

 have been advanced on the subject ; but probably M. 

 Leon Dufour is the only eminent entomotomist, of the 

 present day, who denies the existence of any kind of 

 circulation in insects.* 



Respiratory System. The necessity for the blood 

 being placed in communication with atmospheric air 

 before ifc is adapted for assimilation with the organic 

 mass, is as indispensable among insects as any other 

 class of animals. We accordingly find an intricate 

 and highly developed system of vessels, pervading, in 

 a multitude of ramifications, every portion of their 

 frame, in a manner very similar to the distribution of 

 the blood-vessels in quadrupeds. The relations, in- 

 deed, between these two systems, as they subsist in 

 the vertebrata, seem, as has been well remarked, to 

 oe completely reversed in the case of insects in the 

 former the blood is the moving and pervasive element 

 in the latter it is the air. The sanguineous fluid 

 bathes almost every part of the cavity of the body ; 

 and being too languid to repair, with sufficient rapi- 

 dity, to a given point to receive its vital principle, it 

 is provided that the latter should be conveyed towards 

 it ; and this is done so effectually, that it can be im- 

 parted, with equal facility, wherever there is a mole- 

 cule of the blood to be decarbonised. 



The organs of respiration may be conveniently 

 considered, as has been done by Kirby and Spence, 



* Lacord. Intro. II. 69. note (3.) 



