THE METAMORPHOSIS. 445 



posterior one, has one joint, and the three anterior ones, in regular 

 rotation, two, three, and four joints. In insects, on the contrary, this 

 variation is distributed throughout the whole order, so that their one 

 toe of each foot exhibits either one, two, three, or four joints : it is more 

 unusual for some toes to have three and others four joints, as is the 

 case among the beetles, for instance, in the Heleromera. 



It is hoped that no one, after this comparative view, will take 

 objection to the explanation of the leg joints ; he will but find a con- 

 formity of insects with birds, to which, in the course of our treatise, 

 we have frequently referred, and he must therefore be necessarily 

 convinced of the correctness of what we have advanced. Birds are in 

 every respect concentrated insects, and insects birds deprived of their 

 internal skeleton. 



FOURTH CHAPTER. 



OF MUSCULAR MOTION. 



261. 



THE collective motions of animals are produced by a distinct system 

 of organs, which we call muscles. With respect to the structure and 

 arrangement of these organs in insects, we have already stated all that 

 was requisite in the third chapter of the preceding division ; we conse- 

 quently consider as known both the structure of the entire apparatus 

 of motion as also of its individual parts, and proceed at once to the 

 consideration of their functions. 



We obtain as the first and chief difference in motions their subdivision 

 into voluntary and spontaneous. 



Under the spontaneous motions we consider all those which are not 

 subject to the influence of the will, and which take place in the insect, 

 from the commencement of its life to its death, precisely in the same 

 manner, and which can never be wholly or for any long period inter- 

 rupted, so long as life is to proceed uninterruptedly. We know, from 

 what has preceded, that all these organs are encompassed by a peculiar 



