68 Breathing System in Insects. 



The blood is light colored, and almost destitute of discs or 

 corpuscles, which are so numerous in the blood of higher ani- 

 mals, and which give our blood its red color. The function 

 of these discs is to carry oxygen, and as oxygen is carried 

 everywhere through the body by the ubiquitous air-tubes 

 of insects, we see the discs are not needed. Except for these 

 semi-fluid discs, which are real organs, and nourished as are 

 other organs, the blood of higher animals is entirely fluid, 

 in all normal conditions, and contains not the organs them- 

 selves or any part of them, but only the elements, which 



Fig. 20. 



Cross Section oj Bee, ajter Cheshire, 



h Heart. Tr. Tracheae. 



St. Stomach. ^a Ganglion. 



d Diaphragm. 



are absorbed by the tissue and converted into the organs, 

 or, to be scientific, are assimilated. As the blood of insects 

 is nearly destitute of discs, having only white corpuscles, 

 which are also found in the digested food, and like the 

 same in higher animals, are amceboid, it is wholly fluid, and 

 is almost wholly made up of nutritious matter. Schonfeld 

 has shown that the blood, chyle and larval food are much 

 the same. 



The respiratory or breathing system of insects has ali-eady 

 been referred to. Along the sides of the body are the 

 spiracles or breathing mouths, which vary in number. The 

 full grown larva has twenty, while the iiTiago has seven 

 on each side, two on the thorax, one behind each wing, 

 and five on the abdomen. The drone has one more on 



