THE THORACIC EXO-SKELETOX. 155 



and metathorax, to which the first abdominal somite, Latreille's 

 segment mediaire, is added in many of the Hymenoptera. 



The nomenclature of the several sclerites which form the 

 walls of these somites is still unsatisfactory and confused. This 

 has arisen partly from the difficulty of defining the limits of the 

 somites, but chiefly from an attempt to make the three somites 

 conform to an ideal type which originated in the mind of 

 Audouin [38 and 39] . Audouin examined the meso- and meta- 

 thorax in a great number of insects, and found the same parts 

 represented, more or less distinctly, in all ; and there is no 

 doubt that the meso- and metathorax, when each has a pair 

 of wings, exhibit a close resemblance to each other. The 

 attempt, however, to identify the sclerites of one with the 

 other is not always successful, and when this process is 

 extended to the prothorax it leads to nothing but confusion. 



Audouin took the most highly- modified wing-bearing seg- 

 ments as his type, and expected to find the same structures in 

 the less highly - modified wingless prothorax. Instead of 

 deriving the more specialised from the more generalised, he 

 set up an ideal highly specialised type and attempted to make 

 the less specialised somites of the body conform to his ideal. 



74. LATREILLE, P. A., ' De quelques Appendices Particuliers du thorax de 

 divers Insectes.' Mem. du Museum, torn, vii., 1821. 



75. MACLEAY, 'An Explanation of the Comparative Anatomy of the 

 Thorax of Winged Insects, with a review of the present state of the 

 Nomenclature of its parts.' Zool. Journ., vol. v., p. 145, 1830. 



76. SCHIODTE, J. C, ' Bidrag til Kundskab om Insekternes Thorax, med 

 fortrinligt Hensyn til Latreille's Theorie om Segment mediaire og til 

 Forekomsten og Fordelingen af Spiracula Thoracica.' Overs. Danske 

 Vidensk. Selskabs Forhandlinger, 1856, p. 135. An English resume" in 

 Ann. Nat. Hist., ser. iii., vol. xv., p. 483. 



77. LOEW, HERMAN, ' Monograph on N. American Diptera,' vol. i., 1886. 



78. HAMMOND, A., 'On the Thorax of the Blow-fly.' Journ. Linn. Soc. 

 Zool., vol. xv., 1879. 



79. GOSCH, C. C. A., ' On Latreille's Theory of " le Segment Mediaire " ' (in 

 English). Schiodte Nat. Tidsskr., Rieke iii., Bd. xiii., 1881-83. 



80. BRAUER, F., ' Ueber das Segment Mediaire Latreilles.' Sitzungb. 

 Akad., Wien.. Bd. 85, 1882. 



81. OSTEN - SACKEN, C. R., 'An Essay on Comparative Chastotaxy.' 

 Trans. Entom. Soc., Lond., 1884. Originally published in Mitth. der 

 Miinchener Ent. Ver., vol. v., 1881. 



