THE HONEY BEE 359 



Air-sacs are found in the abdominal region. These are expanded 

 portions of the tracheae and probably make the bee lighter as it flies, 

 for the bee can apparently increase and decrease the size of the air-sacs 

 at will. There are tiny valves in the spiracles and the bee takes in and 

 expels air by expansions and contractions of its abdomen. Hairs sur- 

 round the spiracles so as to prevent dust from entering* The rate of 

 respiration increases with the fatigue of the insect. Air is carried di- 

 rectly to the tissues through the tracheae so that no lung system is 

 needed in which blood and oxygen must mix. 



THE EXCRETORY SYSTEM 



There are Malpighian or urinary tubules (Fig. 234, A) which are 

 long, fine, hair-like structures, opening into the anterior end of the in- 

 testine. These are the excretory organs. Excretions are taken from 

 the blood in the form of urates, and pass through these urinary tubules 

 to the intestine from whence they are thrown out of the body with the 

 faeces. 



THE NERVOUS SYSTEM 



The nervous system (Fig. 214, 235) of the bee is made up of a chain 

 of paired ganglia with two groups of smaller ganglia. The first are 

 called the stomatogastric and the latter the sympathetic ganglia, re- 

 spectively. These ganglia are made up in turn of seven masses of nerve 

 tissue : two in the head, two in the thorax, and five in the abdomen. 



Each mass is composed of two ganglia which lie side by side, and 

 these ganglia are connected with the mass in front and behind by two 

 nerve cords. Only the brain (the most anterior pair of ganglia) also 

 called the supraoesophageal ganglia, lies dorsal to the digestive tract. 



The compound eyes, the ocelli, the antennae, and the labrum, are 

 connected with the brain by nerve twigs, while the mandibles, labium, 

 and other mouth-parts are connected with the suboesophageal ganglion 

 lying directly beneath the oesophagus. 



The most anterior ganglia in the thorax innervate the muscles of 

 the first pair of legs, while the posterior thoracic ganglion is larger and 

 composed of several ganglia which have grown together. From the 

 fore part of this latter ganglion, nerves run to the fore wings and middle 

 pair of legs, while twigs from the posterior portion of this, same ganglion 

 pass to the hind wings and legs. 



The organs and walls of the abdominal region are supplied by 

 twigs from the various abdominal ganglia; but, as with most animals, 

 the more posterior abdominal ganglia are the larger. 



The stomatogastric portion of the nervous system is composed of 

 many small ganglia which are in direct connection with the organs of 

 digestion, circulation, and respiration, while the sympathetic nervous 



