358 



GENERAL BIOLOGY 



The heart, or dorsal vessel, is a tube in the median dorsal region 

 just below the surface, closed posteriorly and open in the head-region. 

 The walls being muscular, the heart contracts at intervals. 



x The blood itself enters through five pairs of ostia, one into each of 

 the five compartments into which the heart is divided. Each compart- 



ment is called a ventricle. Each 

 contraction sends the blood toward 

 the heart. There are valves which 

 prevent it from flowing backward. 

 It then passes through the various 

 spaces in the body to bathe the tis- 

 sues. As the blood passes ventrally, 

 it is gathered into the pericardia! 

 sinus, and when the muscles sur- 

 rounding this sinus contract, the 

 blood is forced through the ostia 

 back into the heart when it is again 

 ready to be sent out. 



Fig 234. 



A. Internal organs of the honeybee, bt., 

 malpighian tubules ; c.s., true stomach ; dv., 

 dorsal vessel ; e., eye ; g., ganglia of nerve 

 chain ; hs., honey sac ; it., rectum ; lp., labial 

 palpus ; mesa, t., mesothorax ; meta, t., meta- 

 thorax ; mx., maxilla; n., nerves. No. 1, 

 No. 2, No. 3, salivary glands ; oe. t oesophagus ; 

 p., stomach mouth ; pro.t., prothorax ; si., 

 small intestine (ileum) ; v., ventricles of dorsal 

 vessel. 



B. Ideal transverse section of an insect. 

 h., dorsal vessel ; i., intestine ; n., ventral 

 nerve-cord ; t.t., stigmata leading into the 

 branched tracheal tubes ; w.w., wings ; a., 

 coxa of one leg ; b., trochanter ; c., femur ; d., 

 tibia; e., tarsus. (After Packard, A, from 

 Cheshire. ) 



THE RESPIRATORY SYSTEM 



Along each side of certain thoracic and abdominal segments there 

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

 ings 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 f in thickness) have thickened rings arranged spirally, and it is 

 these rings which keep the tubes open. 



