116 THE ANATOMY OF THE HONEY BEE. 



metathorax (although the first is often regarded as prothoracic), 

 Avhile the other eight are situated on the sides of the first eight 

 abdominal segments — in the bee on the lateral parts of the terga 

 (figs. 32 and 33, Sp). The breathing apertures are usually pro- 

 vided with a closing apparatus of some sort consisting of the swollen 

 lips of slitlike spiracles, of a small lid, or of a flexible and collapsible 

 chitinous ring, each with special occlusor muscles attached. In the 

 bee a chitinous band surrounds the tracheal tube opening at each 

 spiracle, a short distance from the aperture, and has two opposite 

 loops projecting on the same side, connected by a muscle whose con- 

 traction approximates the two halves of the band so as to close the 

 lumen of the trachea." It is supposed that after an inhalation the 

 spiracles are closed momentarily, so that the first force of the ex- 

 })iratory contraction of the abdomen is exerted against the air shut 

 in the trachetc. with the result of driving it into the extreme tips 

 of the latter — the spiracles then opening, the rest of the contraction 

 is expended in exhalation. 



The internal tracheal system consists, among insects generally, 

 of a large tracheal trunk lying along each side of the body, connected 

 by short tubes with the spiracles and by transverse commissures Avitli 

 each other, while they give off segmental branches into the body 

 cavity which ramify minutely upon the organs and tissues. In the 

 thorax specially large tubes are given off on each side to the legs 

 and to the bases of the wings, while in the head others go to the 

 eyes, antennae, and mouth parts. The whole body is thus virtually 

 a lung with ten pairs of openings along the sides. 



The tracheal system of the bee (figs. 1, 50, and 51) is best developed 

 in the abdomen, where the longitudinal trunks are enlarged into two 

 enormous lateral air sacs (TraSc), Avhich are of greatest diameter in 

 the anterior end of the abdomen. They are segmentally connected by 

 large transverse ventral commissures (fig. 51, TraCorn), most of which 

 are themselves distended into small air sacs. Dorsally the lateral 

 sacs give off in each segment a large tube which divides into two sac- 

 culated branches (figs. 49 and 50, HtTraSc) that enter the pericardial 

 chamber and supply the heart and pericardial cells with trachea^. In 

 the thorax a large sac lies on each side of the propodeum (figs. 1 and 

 50, 7), which bears a short tube opening to the first abdominal 

 spiracle (figs. 21 and 50, ISp). Above these sacs is a narrow trans- 

 verse median one (figs. 1 and 50, cS') occupying the large cavity of 

 the turgid mesoscutellum (fig. 21, ScJ.,). In the ventral part of the 

 thorax there is a large median posterior sac (figs. 1, 50, and 51, 5) 



Tor a detailed doscription of the spiracles in the bee and their occlusor 

 apparatus see Djathchenko (1906). 



