NO. 12 FLYING APPARATUS OF BLOW-FLY RITTER 29 



the angle this axis makes with the horizon varies between about 

 30 and 60 degrees. Also the direction (inclination) of the down- 

 stroke varies. The upper observed limit was 90 degrees. The lower 

 loop of the 8 is, as already stated by Lowne (1890-1895, p. 204), 

 considerably larger than the upper loop. I must remark, however, 

 that I have never observed such an inclination of the 8 as Lowne 

 describes, that indeed it would be contradictory to the observations 

 I have made on the mechanism of the wing-beat described below. 

 The direction of the wing-stroke is also incorrectly represented in 

 Lowne's figure; von Lendenfeld's (1881, p^ 368) accords better 

 with my observations. As is incontestably shown in my kymo- 

 graphic curves (pi. 16, figs. 42, 43, 44), the movement of the wing 

 whilst describing the lower curve of the 8 is, relative to the insect, 

 a movement forward, and not, as Lowne says, a movement back- 

 ward. The upper part of the 8, on the other hand, is described by 

 the wing moving backward. 



At rest the wings lie back upon the abdomen, projecting about 

 a third of their length beyond it. When the insect wishes to fly 

 it moves the wings (wing tips) somewhat forward."" and at the same 

 time raises them. Then it makes a little jump and commences to 

 describe the figure 8 with the wing tips. Both wings are expanded 

 nearly horizontally and moved simultaneously almost vertically down- 

 ward so that they press downward upon the air with their entire 

 surface. The unsupported anal portion of the wing remains some- 

 what behind, because it cannot overcome the resistance of the air 

 so easily as the strongly supported anterior portion. That the wings 

 are held nearly horizontally during the downstroke (it being under- 

 stood that the insect is flying horizontally) is clearly shown by the 

 kymographic figures (pi. 15, fig. 41; P^- 16, figs. 42, 43, 44), par- 

 ticularly in the curves made by a wing, the tip of which had been 

 nipped off. These curves are not described by a point (the tip of 

 the wing), but by a line (the transverse section of the wing along 

 which the tip had been cut off). During the downstroke this line 

 described a broad band, or, since only the veins leave a distinct 

 mark, two parallel Hues corresponding to the only two veins, Ilaa 

 and Iliha, which extend so far toward the tip. Arrived below, the 

 wing glides horizontally forward and then turns, the marginal vein 

 being in front, upward and backward. In this phase the torsion of 

 the wing is at its minimum. The anal border follows the path of 



^ See the chapter on the function of the muscles. 



