PAETS OF THE THORAX. li- 



the insect, namely the thorax. This important part bears all the 

 instruments of locomotion, whether they be legs or wings ; and 

 is most wonderfully constructed for the pm-pose, being supplied 

 in- the interior with hard projections that are needed for 

 supporting the powerful muscular apparatus needful for flight, 

 and the less powerful, but still important system by which the 

 legs are moved. 



The thorax is internally divided into three parts, which we 

 call prothorax, or front thorax ; mesothorax, or middle thorax ; 

 and metathorax, or hinder thorax. Beginning with the pro- 

 thorax, we find it again divided into two portions, the upper 

 and the lower — the former going by the name of pronotum, i.e. 

 in front of the back, and the other called presternum, i.e. in 

 front of the breast. Fig. 7 shows the pronotum of the Stag 

 Beetle : 7aa are the lateral margins, 76 is the anterior margin, 

 Ico are the posterior angles. Id the posterior margin, and 7ee 

 the anterior angles. 



Next we come to the presternum, which is shown at Fig. 8 ; 

 8a being the sternum, and 866 the insertion of the coxa, a joint 

 which will be presently described. 



The mesothorax with the abdomen is shown at Figs. 9 and 10, 

 the former exhibiting the upper, and the latter tlie under sur- 

 face. In the last figure, a is the metasternum, 6 the abdomen, 

 c t]\e parapleura, or side-pieces (sometimes called paraptera, 

 because they are situated by the wings), and d the episterna, 

 or breast-pieces. 



Each of these portions is set apart for a definite use, and is 

 employed for the attachment of some portion of the locomotive 

 apparatus. 



The presternum is used to carry the front pair of legs, as 

 can be seen by looking at the under side of any large Beetle, 

 or indeed of any small one, by the aid of a magnifier. 



The mesothorax bears the elytra, or wing cases, and the 

 intermediate pair of legs, the former being attached to the 

 upper part, or mesonotum, and the latter to the lower part, or 

 mesosternum. The reader must remember that the word 

 * sternum ' always signifies the breast, or under side of the 

 thorax, and ' notum ' the back, or upper side. Lastly, the 

 mesothorax bears the lower, or membranous, wings and the 

 last pair of legs. As before, the wings are attached to the 



