No. l6.] INSECTS OF CONNECTICUT. 20, 



as cerci, caudal setae, claspers, ovipositors, stings, and cornicles 

 or honey tubes. 



INTERNAL ANATOMY. 



The muscles are transparent and colorless, or of a yellowish 

 white color, those moving the body segments being fastened to 

 the body wall. These muscles are very strong, and are capable 

 of rapid motion. Physicists have estimated that certain gnats 

 move their wings at the rate of 15,000 times per second, the 

 estimate being based upon the pitch of the musical note produced. 



Insects breathe through a series of openings called spiracles, 

 along the sides of the thorax and abdomen. Each segment 

 bears two of these spiracles, one on either side, and the open- 

 ings, though often simple, are sometimes provided with valves 

 or fringes of hair to keep out the dust. Connecting with the 

 spiracles are a series of air tubes or tracheae which ramify 

 through the body of the insect. Aquatic insects are provided 

 with special devices for respiration, most immature forms having 

 tracheal gills, but in a few dragon-flies and some stone-flies 

 tracheal gills are retained throughout the insect's existence. A 

 mosquito larva has a tube at the posterior extremity of the body 

 which is protruded from the surface of the water for the pur- 

 pose of obtaining air. Certain aquatic Hemiptera called back- 

 swimmers and water-boatmen carry down bubbles of air under 

 their folded wings. 



The blood is a thin, watery fluid, and does not flow through 

 a system of closed tubes, as in the higher animals, but fills the 

 entire body cavity not occupied by other organs. There is a 

 single longitudinal blood vessel above the alimentary canal, 

 pulsatile in its posterior part, and provided with valves which 

 permit the blood to move only toward the anterior extremity 

 of the vessel, where it is discharged into the body cavity. 



The alimentary canal is a tube extending through the body. 

 In adults this is much longer than the body, and is more or 

 less folded, but in caterpillars it is only a straight tube reaching 

 from one end of the body to the other. Fatty tissues make 

 up a large portion of the contents of the body cavity. 



The nervous system in insects is more highly developed than 

 in other invertebrates. A large ganglion in the head is ana- 

 logous to the brain of vertebrates, and is connected with a series 



