292 THE MECHANICAL FUNCTIONS. 



In the Hymeiioptera, this incision is so deep as to 

 leave only a narrow pedicle, like a neck, connecting 

 these two divisions of the body. In some, this 

 pedicle is short ; in others, long : in the former case, 

 an exceedingly refined mechanism is resorted to 

 for effecting the necessary movements in a part so 

 bulky compared with the narrowness of the surface 

 of attachment.* 



Insects in their perfect state have constantly six 

 legs, which are the developements of the six proper 

 legs of the same animal in its larva condition ; all 

 the spurious legs having disappeared during its 

 metamorphosis. We have seen that in the Myria- 

 poda^ the result of developement is an increase in 

 the number both of segments and of legs ; the 

 reason of which is that, being terrestrial animals, a 

 lengthened form was more useful and accordant 

 with their destination ; but in winged insects, where 

 the object is to procure the means of flight, the 

 organs require to be concentrated, and all super- 

 fluous parts must be retrenched, and discarded from 

 the fabric. The multiplication of organs, which, in 

 the former case, indicated the progress of a higher 

 developement, would in the latter have been the 

 source of imperfection. As long as the insect re- 

 mains in its larva stage, its condition is analogous 

 to that of the myriapode : but in the more elevated 

 state of its existence, its structure is subject to new 

 conditions, and regulated by new laws. 



While the number of members is thus reduced, 

 ample compensation is given by their increased 



* For the details of this structure I must refer to writers on ento- 

 mology, and in particular to Kirby and Spence's " Introduction to 

 Entomology," vol. iii. p. 701. 



