OF MUSCULAK MOTION. 459 



least in those insects in which no such preponderance of the abdomen 

 can occur, partly from its smallness, as in the Hies, and partly on account 

 of its thinness and lightness, as in the Libellulce, we observe no such 

 obliquity during flight : whereas in other insects in which the abdomen 

 itself is heavier, for instance, in the Bo?nbi and wasps, we observe a similar 

 posture, yet its greater weight does not incline the thorax from its hori- 

 zontal position, but the abdomen alone, which is affixed at one small spot, 

 hangs down. In other insects, again, in which the very long and also 

 heavy abdomen forms by far the most considerable part, it is placed in 

 such a position as not to incline the thorax during flight considerably 

 from its horizontal position. Among these is found the genus Fcenus ; 

 which raises, during flight, the abdomen with, in the larger species, its 

 very long ovipositor, perpendicularly upwards, or even sometimes bends 

 it forwards, so that the chief pressure is directed towards the centre of 

 the body. But there requires less strength to advance the thus pressing 

 abdomen, than if, stretched directly out, it drew the entire body down- 

 wards, and daily experience can teach us how much more easy it is 

 to balance a long stick upon the flat hand or the tip of a finger, than 

 to carry it with an extended arm. Most external organs adapt them- 

 selves to the same law, for the legs are in general contracted to the 

 body, and but very rarely stretched out posteriorly. But the antennae 

 appear always to maintain their extended position during flight, but 

 which position is transformed in the Ceramby tides, furnished with long 

 antennae, into a gentle curvature inclining outwards and backwards. 

 In this position they contribute much to maintain an equilibrium with 

 the abdomen, that it may not sink still lower. 



This inclining posture of the whole body is, however, of no conse- 

 quence to the execution of flight, but the likewise oblique attachment 

 of the wings to the thorax is especially so. This oblique attachment 

 is distinctly seen if a line be drawn through the direction of their 

 affixion, and this is conceived to lie in the plane of the axis of the 

 thorax when both are found to cut closely behind the thorax, and even 

 sometimes upon its posterior limits *. The wings consequently during 

 flight do not move perpendicularly to the body, but on an oblique plane ; 

 and are also acted obliquely upon by the pressure of the air, so that 

 upon rising they appear bent upon the posterior margin, and upon 

 sinking they also appear raised. This difference of osture is occasioned 



* See Plates IX. XIV. 



