320 



COLLEGE ZOOLOGY 



its way through spaces (haemoccel) to the ventral part of the 

 body, and thence to the pericardial sinus just beneath the heart. 

 The muscular diaphragm of the pericardial sinus forces the blood 

 through the ostia into the heart. 



Respiration (Fig. 242). — The honey-bee breathes through 

 seven pairs of lateral openings called spiracles, one pair in the 

 prothorax (1 Sp), one in the metathorax (I Sp), and five in 

 the abdomen (777 Sp, VII Sp). The spiracles open into tubes 



called trachea (Tra) which branch and 

 carry air to all parts of the body. Cer- 

 tain tracheae are dilated to form air 

 sacs (TraSc), which are supposed to be 

 of value during flight, since they can be 

 enlarged at will and the specific gravity 

 of the insect correspondingly decreased. 

 Figure 243 shows the trachea to consist 

 of a tube of a single layer of cells (a) 

 lined with chitin which is thickened 

 so as to form a spiral thread. This 

 chitinous lining keeps the trachea open. 

 Each spiracle is provided with a valve 

 which helps prevent the entrance 

 of dust. Oxygen is carried directly 

 to the tissues by the tracheae and does 

 not need to be transported by the 

 blood. 



excretory organs are long, thread-like 

 tubes called malpighian tubules (Fig. 241, bi). They pour their 

 excretions into the intestine at the point where it joins the 

 stomach. 



Nervous System. — There is a complicated bilobed ganglionic 

 mass, the brain, in the dorsal part of the head. Nerves connect 

 the brain with the compound eyes, ocelli, antennae and labrum. 

 The brain is connected by nerve-cords with the subcesophageal 

 ganglion which lies beneath the oesophagus in the head. This 



Fig 243. — Portion of a 

 trachea. a, cellular wall ; 

 b. nuclei. (From Packard, 

 after Leydig.) 



Excretion. — The 



