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 Diptera. 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 must 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, owing 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 Linnzus 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 Ants will suffi- 
ciently shew how the pieces of the thorax may be completely soldered together 
almost into one mass. 
