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 
Fic. 20. 
Cross Section of Bee, after Chesh've, 
h Heart. Tr. Trachex, 
St. Stomach. ga 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 ameeboid, 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 already 
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 imago has seven 
on each side, two on the thorax, one behind each wing, 
and five on the abdomen. The drone has one more on 
