Page:Jardine Naturalist's library Entomology.djvu/161

Rh 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. LeonLéon [sic] 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 it 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, indeed, between these two systems, as they subsist in the vertebrata, seem, as has been well remarked, to be 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 rapidity, 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 imparted, with equal facility, wherever there is a molecule of the blood to be decarbonised. The organs of respiration may be conveniently considered, as has been done by Kirby and Spence,