Thorax in winged Insects. 157 



sects, particularly of the analogous orders Hymenoptera and Diptera. 

 But a little study of their structures will point out the nature of such 

 aberrations, and I repeat that the above is the most correct mode of view- 

 ing an insect. Even coleopterous Annulosa, such as a Curculio or Ce- 

 rambyx, * may be reduced to the same law of structure, the posterior 

 abdominal segments of their larvse being converted more or less into 

 parts of the organs of generation. One of the most beautiful facts that 

 the study of comparative anatomy presents us with, is the delight Nature 

 appears to take in working as it were with a given quantity of material, 

 while she neveitheless produces an infinite variety of forms. 



The developement of the various segments of the body of annulose 

 animals forms another consideration, and a most important one. If the 

 developement of each segment be tolerably uniform, we have the great 

 majority of worms and larvae. If, on the contrary, the developement of 

 the thirteen segments be irregular, we have the majority of perfect insects, 

 Arachnida, and Crustacea. In general we may add, that if any one of 

 the three principal parts of the body be greatly developed, the general 

 size being given by the full grovra larva, tlien one or both of the remain- 

 ing parts must be proportionably small in the perfect insect. This in- 

 deed clearly amounts to a truism : and therefore, taking the size of the 

 larva as a limit, we cannot be surprised that the head and abdomen of an 

 Evania, for instance, are so small when the developement of its thorax is 

 so great. 



The object of my present investigation shall be the thorax f of a winged 

 insect. It is here that M. Audouin has particularly distinguished himself 



» I have not alluded in the text to Mr. Kirby's tables, given pp. 703 and 704 

 of his third volume, or to his previous description of the abdomen in insects, 

 because in some cases they are founded on imperfect examination, and in others 

 on that deficiency of generalization which I cannot help thinking the learned 

 author was solicitous should characterize his worJi. 



f Fabricius in his "Philosophia Entomologica" has called this part the truncus, 

 an expression which implies the whole body withoutthe head and limbs. Being 

 thus objectionable, the term seems never very generally to have come into use ; 

 and in fact becomes quite unnecessary if we divide the thorax into protkorax, 

 mesothorax , and metathorax. M. Audouin, therefore, has discarded it as use- 

 less as well as objectionable. See Ann. des Sciences Naturelles, Vol, I. p. 119. 



