24 



CALIPOBNIA STATE COMMISSION OF IIORTIClH/rURE. 



The rirculalion of insects is as yet im- 

 perfectly understood. The blood is cold, 

 and, except for a slight yellowish tint, is 

 colorless. There is no system of closed 

 blood vessels, as in the higher animals, 

 but the blood is forced through the body 

 cavities by an organ which represents 

 the heart. This organ is a delicate tube, 

 located in the upper surface of the body, 

 and is usually called the dorsal vessel. 

 This represents the heart, and ordinaril-y 

 consists of eight sections, or sacs, which 

 open into each other and which, by con- 

 tracting, drive the blood forward to the 

 region of the head, where it escapes into 

 the body cavity. No system of arteries 

 or veins has been traced. In its course 

 through the body, the blood becomes 

 oxygenated by contact with the respir- 

 atory organs, which penetrate into all 

 parts of the body. (See Fig. 27.) 



TJie respiratory system- consists of a 

 vast number of tubes or trachea', which 

 have their openings to the outer air 

 along the sides of the insect. These air 

 tubes are known as spiracles or stigmata. 

 They are usually placed on each side 

 of every segment, excepting the head, 

 and communicate with a main tracheal 

 trunk which extends along the sides of the body. One of these trunks 

 is situated on each side and from these the trachea' branch off in all 



FIG. 28. Tnu'huiil system of an insect. 

 a, antenna; b, brain; I, leg; n, nervi' 

 cord; p, palpus; ,s, spiracle; »(, spiracu- 

 lar, or stigniatal, branch; <, main tra- 

 cheal trunk; I', ventral brancli ; rx. vis- 

 ceral brand). (After Kolbe.) 



Trachea opened. Trachea closed. 



FIG. 29. Apparatus for closing the spiraculnr trachea in a beetle (Ln- 

 eanus). b, bow; bd, band; c, external cuticula; I, lever; m, muscle; 

 •f, spiracle ; r, trachea. (After Jndeich and Nitsche). 



directions until the whole body is permeated with these delicate air 

 tubes and thoroughly aerated. 



