Page:How to Keep Bees.djvu/233

Rh of air tubes, termed tracheae, which carry the air to all parts of the body. When the body of an insect is opened, the tracheae appear as silvery threads, on account of the contained air. In the adult honeybee certain of the tracheae are greatly expanded so as to form large air sacs. (Plate XXVI 6, 2).

The glands,—Those glands found in the body of the honey bee that are of most interest to the practical bee-keeper are the following:

In the larva there is a pair of long, tubular glands, which secrete the silk of which the cocoon is made. These glands open through a common duct, which has its outlet near the mouth.

In the adult worker bee there are four pairs of glands opening into the mouth, which have been much discussed by students of this subject. These glands are designated both by number and by name as follows: System I. or supracerebral glands; system II. or postcerebral glands; system III. or thoracic glands; and system IV. or mandibulary glands.

The supracerebral glands or system I. (Plate XXV, Fig. 4, 1) are situated in the head above the brain. They open by two openings in the floor of the mouth cavity, one on each side.

The postcerebral glands or system II. (Plate XXV, Fig. 4, 2) are situated in the head behind the brain; their outlets unite into a common duct which opens on the middle line of the anterior end of the oesophagus at the base of the tongue.

The thoracic glands or system III. (Plate XXV,