OF THE MUSCLES. 179 



the same in every animal, from man to the most minute 



animalcule. The attachment of muscle is solely to the 



^osseous^, plates or bones, which constitute the external 



- ^ 



covering of an insect ; in these they originate precisely in 

 the same manner as the muscles in the human frame are 

 attached to, and originate in, the bones. 



The bulk and form of muscles in insects are beautifully 

 apportioned to the offices they are required to perform ; 

 and unusual bulk in any part of an insect generally implies 

 the presence of unusually developed muscle, and the object 

 for which it is developed may frequently be ascertained. 

 We have before seen, that the fore wings arise from the 

 mesothorax, and the hind wings from the metathorax: 

 these segments vary greatly in size, and this variation de- 

 pends so precisely on the powers of flight possessed by 

 each pair of wings, that an insect anatomist, on regarding 

 these two segments alone, would at once decide on the 

 relative power of the wing which they had borne. In flies, 

 the fore wings alone are used in flight ; the hind wings are 

 rudimental ; the whole bulk of muscle, therefore, required 

 for flight, is placed in the mesothorax : in beetles the hind 

 wings alone are used in flight, and the bulk of muscle is 

 consequently transferred to the metathorax. It happens 

 in some moths, that one sex flies and the other does not ; 

 and in these the different size of the wing-bearing seg- 

 ments proves the provision of muscle to be for the pur- 

 pose of flight. In the common ant, the little worker 

 never leaves the ground ; wings, therefore, would be an 

 incumbrance to it. We find that its pro- meso- and meta- 

 thorax are very small and insignificant segments, while 

 the mesothorax of the productive female is the largest seg- 

 ment in her body, because it is one of her duties to perform 

 a long flight, and to use the wings which that segment 

 bears. The muscles in those wing-bearing segments which 



N2 



