The blood is light colored, and almost destitute of discs or corpuscles, which are so numerous in the blood of higher animals, 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 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 themselves or any part of them, but only the elements, which 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 these discs, it is almost wholly fluid, and is almost wholly made up of nutritious substance. [Illustration: Fig. 8. _Nervous System of the Drone magnified four times._] 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. These are armed with a complex valvular arrangement which excludes dust or other noxious particles. These spiracles are lined with a delicate membrane which abounds with nerves, which were referred to in speaking of them as smelling organs. From these extend the labyrinth of air-tubes (Fig. 2, _f, f′_), which breathe vitalizing oxygen into every part of the insect organism. In the more active insects--as in bees--the main tracheæ, one on each side of the abdomen, are expanded into large air-sacks (Fig. 2, _f_). Insects often show a respiratory motion, which in bees is often very marked. Newport has shown that in bees the rapidity of the respiration gauges the heat in the hive, and thus we see why bees, in times of severe cold, which they essay to keep at bay by forced respiration, consume much food, exhale much foul air and moisture, and are liable to disease. Newport found that in cases of severe cold there would be quite a rise of mercury in a thermometer which he suspended in the hive amidst the cluster. In the larva state, many insects breathe by fringe-like gills. The larval mosquito has gills in form of hairy tufts, while in the larval dragon-fly the gills are inside the rectum, or last part of the intestine. This insect, by a muscular effort, draws the water slowly in at the anus, when it bathes these singularly-placed branchiæ, and then makes it serve a further turn by forcibly expelling it, when the insect is sent darting ahead. Thus this curious apparatus not only furnishes oxygen, but also a mode of motion. In the pupa; of insects there is little or no motion, yet important organic changes are taking place--the worm-like, ignoble, creeping, often repulsive larva, is soon to appear as the airy, beautiful, active, almost ethereal imago. So oxygen, the most essential--the _sine qua non_--of all animal food, is still needed. The bees are too wise to seal the brood-cell