1868.] PARKES — RESPIRATION OF INSECTS. 421 



unique means by which it is effected in the insect race. In all 

 other animals, whether low or high in the scale of being, 

 wherever there is a circulation of the blood, or nutritive fluid, 

 and as a consequence, some organ of propulsion termed a heart, 

 this blood is sent continually to some special region of the body, 

 where an apparatus is set apart for its constant renewal, 

 termed lungs, in reptiles, birds and mammals, and gills, in 

 fishes. Thus, all the blood in the body of a fish is brought suc- 

 cesssively, through a delicate net work of vessels which spread 

 over the gills, into direct contact with the water which bathes 

 every portion of such gills ; and thus the interchange of gases we 

 have referred to, takes place. In the various terrestrial animals, 

 however, lungs of different kinds are provided, and to these the 

 blood is constantly sent, to receive the necessary aeration. 



Perhaps we should also remark still further that, according to 

 the peculiar habits of each class of animals, according to 

 the slowness or activity of their movements and the feebleness or 

 vigour of their vascular system, so are their lungs or respiratory 

 organs modified. For instance, in the cold-blooded and slow 

 moving Reptile class, the lung is little more than a simple bag, 

 with a few air chambers lining its interior ; and thus the blood, 

 which flows through the vascular net-work lining these chambers, 

 is somewhat slowly brought in contact with the air which is 

 inspired. 



On the other hand, in the case of birds and mammals whose 

 muscular system is called into active and vigorous play, we find a 

 most effective and elaborate arrangement, consisting of an almost 

 innumerable aggregation of elastic air cells, over the walls of 

 which is spread an immense surface of capillary net-work ; so that, 

 at every fresh inspiration, a considerable portion of the animal's 

 blood is exposed to atmospheric influence. 



Now of all the diversified grades^ of animals, that add variety, 

 beauty, vivacity and utility to the wondrous planet on which we 

 live, there is no one class which exhibits such marvellous evidence 

 of muscular force, and untiring activity as the class Insecta. We 

 might therefore — reasoning from analogy — have expected to find 

 a most elaborate system of arteries and veins, conveying their 

 blood to and from an equally elaborate and vigorous respiratory 

 organ. Instead of this, however, we find a sudden and startling- 

 break, in what appeared to be the uniform and universal organic 

 arrangement, ordained for the performance of this function ; a 



Vol III. Z No 6. 



