Thorax in winged Insects. 159 



will be proportionably small, as in Coleoptera; and if, on the other 

 hand, the mesothorax be much developed, we have the prothorax small, 

 as in Hymenoptera and Biptera. From these principles it follows that 

 the mesothorax of a beetle is to be considered as composed of the third 

 segment of the larva evanescent, while the metathorax consists of the 

 fourth segment of the larva developed. But these two segments have 

 each a pair of wings as well as of feet, which shews an exceeding power 

 of developement in the third and fourth segments of a winged insect. 



It raust not be imagined that the pieces of the thorax mentioned in the 

 above table are all present and distinct in every insect. Pieces of the 

 thorax may disappear by being evanescent, ovnng to the great develope- 

 ment of the contiguous segments, or by being confluent, or soldered to- 

 gether with the next adjoining pieces.* To know the pieces which are 

 thus lost, it might be thought that on comparing the larva with the per- 

 fect insect the position of the stigmata ought to afford some clue, but in 

 truth these are unsafe guides, as it is well known that the situation of the 

 stigmata in the perfect insect varies very generally and considerably 

 from what it was in the larva. 



The prothorax of a beetle is not always so complex in its structure as 

 the mesothorax and metathorax, some of the pieces of the tergum being 

 almost always evanescent. The tergum of the prothorax seems most 

 ordinarily in winged insects to consist of half the number of pieces that 

 compose the terga of the mesothorax and metathorax, taking all three at 

 their maximum of developement. In other words, the tergum of the 

 prothorax in general appears to consist of only two pieces. But looking 

 at Orthopterous genera, such as Locusta or Gryllus, or at certain Annu- 

 losa, where the tergum of the prothorax undergoes its maximum deve- 

 lopement, we can discover all its four divisions. In Coleoptera, if one 

 or two of the pieces be not evanescent, they are at least all confluent, so 

 as to form one conspicuous segment, which is the thorax of Linnseus and 

 Fabricius. In certain genera of this order, however, the typical compo- 

 sition of the tergum of the prothorax is more or less distinct; the only 



* The Hymenopterous genus Cryptocerus and several other Ant.i will suffi- 

 ciently shew how the pieces of the thorax may be completely soldered together 

 almost into one mass. 



