THE HONEYBEE AND BEES IN GENERAL 



243 





forces the olood from the ventral part of the body into the sinus, 

 and thence through the ostia into the heart. 



THE RESPIRATORY SYSTEM (Fig. 135). The honeybee breathes 

 through openings, called spiracles (sp.), situated in the sides of cer- 

 tain thoracic and abdominal segments. No air enters through 

 apertures in the head, as in 

 vertebrates. There are two 

 pairs of spiracles in the thorax, 

 one in the sides of the pro- 

 thorax, the other in the meta- 

 thorax. Five pairs are present 

 in the abdomen. The spiracles 

 open into tubes, called trachea. 

 These unite with longitudinal 

 tracheae which extend along the 

 sides of the body. Other tra- 

 cheae arise from these longitu- 

 dinal trunks and distribute their 

 branches to all parts of the 

 body. The tracheae (Fig. 136) 

 are tubes composed of a single 

 layer of cells (a) and lined with 

 a thin chitinous wall. This wall 

 is thickened at regular inter- 

 vals, forming a spiral thread, 

 which serves to keep the tra- 

 cheae open. Certain tracheae 

 are dilated into air sacs (Fig. 

 135), the largest of which are situated in the anterior part of the 



F IG - 135- Respiratory system of worker bee as seen from above, one ante- 

 rior pair of abdominal sacs removed and transverse ventral commissures 

 of abdomen not shown. / Sp., Ill Sp., VII Sp., spiracles; Ht. Tra. Sc. y 

 Tra.Sc., i, 2, 4, 7, 8, 10, tracheal sacs; Tra., tracheae. (From Snod- 

 grass, Technical Series 18, Bureau of Entomology, United States De- 

 partment of Agriculture.) 



FIG. 136. Portion of a trachea, a, 

 cellular wall. (From Packard 

 after Ley dig.) 



