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92 NATURAL HISTORY OF WASPS. 
and meta-sternum. ‘The wings mark by their insertion 
the division between the sternal and scutal regions. 
The prosternum we have already seen. The sternal 
portion of the meso-thorax, called, according to this 
simple fnomenclature, the meso-sternum, is repre- 
sented by a large convex plate, marked in the 
smaller wasps by a bright yellow triangular spot. 
The lower end of this plate seems to slope back- 
wards into a point which bears the middle pair of 
legs, while the fore-wings, with their little yellow 
wing cover, or tegula, are attached at the upper part. 
Just below and rather in front of the wing cover, in 
the line which separates the pro-thorax from the 
meso-thorax, the first part of thoracic spiracles open 
by a curvi-linear orifice which is not readily dis- 
tinguishable without a little practice, notwithstand- 
ing its large size. : 
The size and general development of each division 
of the thorax bears a close relation to the size of the 
appendages which it supports. In wasps and butter- 
flies the front pair of wings is the largest; so the 
meso-thorax is more developed than the meta-thorax 
which bears the hind wings. In beetles, which carry 
their wings on the meta-thorax, and the wing-covers 
only, which we must not confuse with the little wing- 
covers of the wasp, on the meso-thorax, these. pro- 
portions are reversed. 
The meta-thorax has the same fourfold division, 
and the same general arrangement of its elementary 
parts as the preceding segments have. The pre- 
scutum is turned in; and the scutum, as in the meso- 
thorax, bears a pair of wings. But, instead of pre- 
senting a broad convex surface, it forms a transverse 
