N0„ 12 FLYING APPARATUS OF BLOW-FLY RITTER 3I 



describes an experiment proving this, which I have repeated in the 

 following manner: From a recently killed fly whose wings are 

 raised, the abdomen and head are removed and the thorax grasped 

 in a broad forceps so that one of the points of the forceps is at its 

 anterior, the other at its posterior end. On compressing the forceps 

 the thorax is shortened just as it is when the dorsal muscle contracts. 

 Thus the forceps' pressure imitates the action of the muscle, and a 

 very slight pressure suffices to cause the wings to descend. The 

 high development of the dorsal muscles readily explains the great 

 force of the downward stroke of the wing. 



That a contraction of the dorsal muscles must lead to a down- 

 ward movement of the wings follows from a consideration of the 

 anatomy of the skeleton. As the convexity of the back is increased 

 by the contraction of these muscles, the process^is prsealaris (pi. 2, 

 figs. 3, 4, pti), as well as the processus postalaris (same figs., ptll), 

 will be raised. By means of the processus postalaris the processus 

 duplicatus of pterale A (pi. 3, fig. 8; pi. 4, fig. 9; dn) is also raised, 

 and the distal processes (processus rostralis and analis), acting as 

 levers, correspondingly depressed. These processes then press the 

 wings downward. 



The dorso-ventral muscles act as antagonists to the dorsal. They 

 compress the thorax in a vertical direction and accordingly act as 

 raisers of the wings. 



The function of the direct muscles was determined as far as pos- 

 sible under the binocular by pulling them with a fine forceps in the 

 direction of their length. In this way the function of most of them 

 could be made out quite clearly. 



The adductor alse (pi. 13, fig. 33, md) draws the wing backward 

 toward the body. It serves to bring the wing back from the position 

 of flight to that of rest. 



The two abductors (pi. 11, fig. 30, mbll ; pi. 13, fig. 33, mbl) 

 draw the wing horizontally forward. One of these two muscles 

 draws the wing when depressed and causes its forward movement 

 during and after the downstroke. 



The two levators (pi. 11, fig. 30; pi. 13, fig. 34, mel, mell) raise 

 the wine:, and at the same time draw it somewhat backward. Their 

 action has a similar effect to that of the dorso-ventral muscles. They 

 are inserted on the processus duplicatus of pterale A, and by their 

 contraction depress that process and thus cause the wing to rise. 



The two supinators depress the anal portion of the wing, and 

 the pronator depresses its anterior border. By the action of these 



