OF MUSCULAR MOTION. 457 



( 176) we have called the dorsal-, lateral dorsal-, lateral- and furcate 

 dorsal-muscles, are those which act in common for producing the respir- 

 atory and volatile motions, and therefore must be examined here more 

 closely as to their effects. One of them, the straight dorsal muscle, 

 which is expanded between the meso- and meta-phragma, acts parallely 

 to the axis of the body ; it arches by its contraction those plates within 

 which it lies, and thereby produces the inflexion of the wing. In 

 insects with connate thoracic segments it is assisted in this function by 

 the oblique, lateral dorsal muscles, which likewise sit quite alone upon 

 the dorsal plate and its processes, particularly the metaphragma. By 

 means of it, therefore, the blow downwards of the wing is produced, 

 and as it also arches the entire thorax, and likewise also distends it, it 

 promotes the inspiration of air. In opposition to them the lateral and 

 furcate dorsal muscles act. By their contraction they approximate the 

 dorsal plate to the sternum, draw it down to the latter, and thereby 

 effect the raising of the wing. They also contract the cavity of the 

 thorax, and thereby promote the expiration of the air. By the alter- 

 nating contraction of these muscles, opposed in their effects, the flap- 

 ping of the wing of insects is produced. It is therefore the result of a 

 distension and contraction of the thorax, in which naturally its lateral 

 radiations, the wings, must immediately participate ; this is another 

 reason for considering the wings as mere continuations of the membrane 

 of the thorax, which, only in consequence of their change of function 

 occasioned by internal respiration, have received their peculiar extensor 

 and flexor muscles. 



If after this very general survey of the mode of flight in insects we 

 look around us for some peculiar divarications of individual orders, we 

 shall find it expressed, especially in the position of the entire body, as 

 well as of its individual limbs. With respect, in the first place, to 

 taking flight, we shall even rind some differences in the manner in 

 which this is executed. Those that likewise possess the power of 

 leaping, namely, the Grylli and Cicada, do it most readily. They 

 raise themselves by a leap from the ground so soon as they may be 

 urged to take flight, then expand their wings already floating in the 

 air, and proceed in the direction already given by the leap. Yet 

 are these insects not good and continuous fliers, with the exception of 

 the migratory locust, but the majority return again to the ground at a 

 very short distance from their place of starting. With the same ease 

 do all other flying insects take wing which bear their wings always 



