THE RESPIRATORY TRACT
Insects have no lungs, and the blood does not carry oxygen about as in the higher animals; air is drawn into the body and brought into direct and immediate contact with the tissues. In the butterfly there are eight pairs of spiracles or breathing-holes—seven pairs in the abdomen and one in the prothorax. These spiracles are connected with large air-sacs reaching from one end of the body to the other, each air-sac being provided with minute branching tubes called tracheae, which carry air directly to the various tissues of the body. The carbon dioxide produced in the respiratory changes passes out through the spiracles, the transfer of gases being produced largely by movements of the abdominal muscles.