360 General Biology 



THE RESPIRATORY SYSTEM 



Along each side of certain thoracic and abdominal segments there 

 appear openings called spiracles (Fig. 215). It is through these openings 

 that the bee breathes. One pair of these spiracles may be found in the 

 prothorax, one pair in the metathorax, and five pairs in the abdomen. 



The spiracles open into little tubes known as tracheae which unite 

 in turn with other tubes running in a longitudinal manner. These longi- 

 tudinal tubes are called the trunks, and from the trunks many branches 

 are given off to all parts of the body. The tracheary tubes (though 

 only one cell in thickness) have thickened rings arranged spirally, and 

 it is these rings which keep the tubes open. 



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 bees 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 

 directly to the tissues through the tracheae so that there is no need for 

 a lung system 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 

 intestine. 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 the following 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. 



