466 WESTWOOD ON THE 



In Ctenophora the mesothoracic scutellum is more distinct, 

 and the metathoracic scutellum more vertical ; these two organs 

 being separated by a distinct transverse piece, which Latreille 

 terras the ** tergum du metathorax," but which in Tipula ole- 

 racea is reduced to a line so slender that it is scarcely per- 

 ceivable. 



Now the segment bearing the piece which I have termed 

 the metathoracic scutellum, is called by Latreille '' le premier 

 segment abdominal," and bearing the " balanciers " — " ayant 

 chacun pres de leur base interne un stigmate ; preuve que ces 

 organes ne sont point des ailes rudimentaires, puisque le meta- 

 thorax, dont ils devraient par analogic faire partie, n'ofFre point 

 de spiracules." — Latr. Coursd'Ent. ; Atlas, p. 17. 



If, however, this were really " le premier segment ab- 

 dominal," it would follow that that part of the body which is 

 generally termed the abdomen would have one joint less than 

 the typical number. It happens, however, unfortunately for 

 this theory, that (contrary to the general but singular rule which 

 prevails amongst insects, by which the perfect insect is deprived 

 of several of the nine abdominal segments which it possessed 

 in the imperfect state,) the Tipula oleracea, Ctenophora, &c. 

 have, in the perfect state, nine distinct abdominal segments, 

 exclusive of the exserted organs of generation. 



From this alone we should be perfectly warranted in regard- 

 ing the " premier segment abdominal " of Latreille as thoracic, 

 and the halteres as representing the lower wings ; "^ indeed, 

 any one who will carefully examine a living Dipterous insect, 

 will be convinced that the latter are intimately connected with 



tinuation of tlie sides of the part bearing the large plate, but upon the dilated 

 and deflexed sides of the following narrow piece ; hence, from analogy with the 

 Hymenopterous metathorax, the piece bearing the spiracles will be the metatho- 

 racic scutellum, and that which bears the posterior scutelliform plate the meta- 

 thoracic scutum. 



,1 Mr. Newman, although considering the halteres as representing the lower 

 wings, and attached to the metathorax, (thus rejecting the views of Audouin and 

 Latreille, as to the posterior portion of the thorax being abdominal,) seems to have 

 adopted their views, by believing that the metathoracic postscutellum, and per- 

 haps scutellum, in MacLeay's figure of Polisfes, are referable to the propodeon or 

 basal segment of the abdomen. {Ent. Mag.Vo\. l.p. 411.j Mr. Haliday has also, 

 still more recently, adopted the views of Latreille and Audouin, by giving the 

 terminal part of the metathorax as the propodeon or basal segment of the abdo- 

 men, {Etit. Mag. Vol. V. p. 211,) although 1 had clearly proved the incorrectness 

 of the supposed non-existence of metathoracic spiracles in my Memoir on the 

 Earwiii. 



