THORAX: MESOTHORAX. 269 



Moreover, in some of the longicorn beetles there is a pair 

 of moveable spines (umbones, Kirby and Spence), arising 

 at the sides of the pronotum ; and in lepidopterous insects 

 there is a pair of scales covered with hair, quite distinct from 

 the wing-covers (tegulae), and which the same authors term 

 patagia, or tippets ; but which have been overlooked by all 

 other authors except Chabrier, who first discovered them, or 

 else confounded (as by Burmeister, p. 77)> with the true 

 tegulse. They are described as vesicles appearing full of 

 liquid and of air, and are placed at the sides of the pronotum. 



2. TheMesothorax (Prothorax, Strauss-Diirckheim), T 2, 

 upper, and (T) 2, under surface. This is the second seg- 

 ment of the thorax (or the first of the alitrunk of Kirby 

 and Spence), and bears the anterior pair of wings, or 

 their representatives, and the middle pair of legs. In 

 insects which have the four wings of equal size, the meso- 

 thorax and the metathorax (the following segment), are 

 equally developed ; but when, on the contrary, one pair of 

 these organs is more particularly developed, the segment to 

 which it is attached is consequently increased in size. If this 

 pair of wings be the anterior pair, the mesothorax is greatly 

 enlarged ; this is, therefore, the case in the Diptera (fig. 126), 

 where the mesothorax almost occupies the entire thorax. In 

 the Hymenoptera (fig. 124), the second pair of wings exist, 

 but of a smaller size than the fore pair ; the metathorax is 

 accordingly more developed than in the Diptera, but is 

 smaller than the mesothorax. If we now look at those orders 

 which have the second pair of wings enlarged, we find the 

 mesothorax diminished, and the metathorax increased in size 

 to a corresponding extent ; this is the case in the beetles, but 

 more especially in the extraordinary parasitic order, Strep- 

 siptera, respecting which so much incorrect matter has been 

 published. 



The four pieces of which the upper side of each thoracic 



A A 3 



