856 



INSECT. 



" more particularly valuable, and, making allowance ' in the perfect insect varies very generally and con- 

 fer the nomenclature of parts, deserves the special j siderably from what it was in the larva." We ha\e 

 attention of entomological students." 



ties. 116, Upper, and 117, under side of the thorax of a beetle 

 (Suprestiji), T 1 pronotum, (T) 1 prosternum, T 2 mesonotum, 

 (T) mesosternum, marked with lines to distinguish its 

 boundary, T 3 metanotum, (.T) 3 mctasternum. H, head; A, 

 abdomen ; w 1, elytra ; w 2, posterior wings. 



Much of this confusion has been obviated by M. 

 Audouin, who, from his admirable comparative inves- 

 tigation of the structure of the segments of the body, 

 ascertained that they were respectively composed of 

 the same essential parts, and consequently that the 

 same series of names might be applied to each. The 

 following is a table of the thorax, as theoretically 

 supposed by him to exist in all insects. 



Thorax. 

 (Truncus, 

 Linn., Kabr. "* 

 and Kirby) 



Prothorax. 



(Manitrunk, 



Kirby ; 



Corselet, 



Strauss) . 



Mesothorax. 

 (Meditrunk, 



Kirby ; 

 Prothorax, 



Strauss. 



Metathorax. 



(Protrunk, 

 f irby & Sp.; 

 Metathorax, 



Strauss.) 



Postscutellum. 



Prothorax, 

 Kirby) T J. 



Pectus. svi 



(Prosternum ( Sternum. or hi 

 Burmeister.-{ E P*t"na. I or 11 

 Antepectus, I . 

 Kirby) (T) 2. VE Pimera. 

 Furca, called Antefurca. 

 Tergum. 



korki 



ba 

 ea 

 Kirby) T2! vrosiscuiei. aord2 



Pectus. 



(Mesoster- (**&*** . 

 num.Burm < Sternum - horh2 

 Medipectus,' I Episterna. 1 or 1 2 

 Kirby) (T) 2. ^ E P ln iera k or k 2 

 Furca, called Medifurca. 

 f Tergum. 



(Metanotum f Pescutum a or a 3 

 Burmeister : J Scutum - b cr b 3 

 Mrtathorax I s ctellum. core 3 

 Kirby.) T 3. VPostscutell.dordS 



by.) (Tj 3 

 Furca, called Postfarca. 



- It must not be imagined, however," observes Mr 

 MacLeay, "that the pieces of the thorax mentioned in 

 the above table are all perfect and distinct in every 

 msect. Pieces of the thorax may disappear, beim> 

 evanescent owing to the great development of the 

 contiguous segments, or by being confluent or sol- 

 dered together with the next adjoining pieces. To 

 know the pieces which are thus lost, it might be 

 lought that on comparing the larva with the perfect 

 'sect, the position of the stigmata (spiracles) ought to 

 afford some clue, but in truth these are unsafe gmdes ; 

 s well known that the situation of the stigmata 



Ti 



115 



120 



Figs. 118, pronotum; 119, mesonotum; 120, metanotum of a 

 Dyticus. In listhe subsegments are confluent. In HQand 120 

 the alternate subsegments are dotted to show their extent. 



indeed found a clue for getting out of the difficulty 

 above-mentioned, but from the little attention hitherto 

 paid to the subject, another difficulty of a not less 

 formidable but of a far more philosophical kind has 

 presented itself, namely, that of proving, by careful 

 study, the relations of the several parts in the differ- 

 ent orders, and the variations they are subject to. 



(T); 



(TJ 2 



IT) 



It 121 



122 



128 



13 



Figs. 121, prosternum; 122, mesosternum; 123, metasternum of 

 a Dyticus. 



The total number of parts in the thorax, according 

 to Audouin, amounts to thirty-six; but if the simple 

 pieces, as the sternum, &c., be supposed to be divided 

 by the medial line, the number will be fifty-two ; and 

 Mr. MacLeay, by supposing that each of the three 

 sterna consists, like the terga, of four transverse pieces 

 similarly divided by the medial line, causes the whole 

 number of pieces in the thorax to mount up to seventy- 

 two. Authors, however, who have looked at the 

 composition of the thorax, without having any theo- 

 retical views to maintain, have found the really dis- 

 tinct number of its parts much fewer in number than 

 either of the last named authors ; thus Chabrier and 

 Burmeisier reckon only eighteen, Kirby and Spence 

 twenty, and Straiiss-Durckheim twenty-two. We 

 will now confine our attention successively to the 

 primary segments of the thorax, and show the chief 

 modifications which they exhibit, and then describe 

 the organs of locomotion. 



1. The Prothorajc (manitrunk, Kirby), T 1 & (T) 1. 



