118 THE ANATOMY OF THE HONEY BEE. 



which gives off trunks to the middle and hind legs and a large sac 

 on each side (fig. 51, 6 and 6) to the ventro-lateral walls of the thorax. 

 Two large strong tubes (figs. 1, 50, and 51, Tra) — the only tracheae 

 in the bee's body well developed as tubes — extend backward from the 

 head through the neck and prothorax to the first thoracic spiracles 

 (figs. 50 and 51, ISp) . Each of these gives off a branch which divides 

 into the trachea for the first leg and into another that connects with 

 the posterior ventral thoracic sac (5). An anterior median thoracic 

 sac {Ji) is connected with the two large anterior tubes near where these 

 enter the neck. In the head are a number of large sacs which are 

 situated above the brain (see figs. 1, 50, and 51, 1), about the bases 

 of the eyes and optic lobes (see figs. 1 and 50, ^), and above the bases 

 of the mandibles j(see fig. 1, 3). 



Nearly all of the tracheae in the bee's body are excessively delicate 

 and their walls mostly lack the spiral thickening that ordinarily holds 

 a tracheal tube open. They are consequently very distensible and, 

 when inflated, they show as opaque glistening white vessels, which, 

 however, when empty, are extremely difficult or actually impossible to 

 see. The smaller branches are so numerous and flabby in the thorax 

 and the legs (fig. 1, LTra) that they appear to form everywhere 

 meshworks or sheets of tiny glistening air-cavities imbedded between 

 the muscle fibers. Only the large trunks in the anterior part of the 

 thorax have the normal tracheal appearance. 



The body of the bee is thus most abundantly aerated, probably 

 more so than that of any other insect. The numerous large and 

 small sacs form great storehouses of air — tanks containing reserve 

 supplies of oxygen. They are not present for the purpose of lighten- 

 ing the weight., of the body, because inflation with air does not 

 decrease the weight of any object surrounded by air. 



The respiratory movements are limited to the abdomen in the bee 

 on account of the solidity of the thorax. They vary a great deal 

 according to the activity of the individual. While sitting quietly 

 at the entrance of the hive or walking slowly about, bees usually 

 exhibit almost no respiratory motion, only a very slight vibratory 

 trembling of the abdomen being noticeable. Others that are walk- 

 ing hurriedly about lengthen and shorten the abdomen very percepti- 

 bly, the motion being specially pronounced at the tip. A bee that 

 has just alighted after flying exhibits still more pronounced abdomi- 

 nal movements, not only a contraction and expansion but an up- 

 and-down motion as well. When a bee is becoming asphyxiated in 

 a killing bottle the extension and contraction of the abdomen is most 

 pronounced, although much slower than in the ordinary breathing 

 movements. 



The muscles of the abdomen that produce respiration have been 

 described by Carlet (1884), who distinguishes seven different sets of 



