140 PHYSIOLOGY OF INSECTS. 



frequently retractile, each within the one preceding it. 

 The twelfth segment, paratelum, is still smaller : in the 

 females of all bees, wasps, and other stinging insects, it is 

 the last segment, the telum not being present in its usual 

 form. The thirteenth, telum or last segment, is usually 

 the smallest of them all ; it is often conical and pointed : 

 in the females of bees, wasps, &c., it is wanting, and its 

 place supplied by a sting. 



Each of these segments has an upper or dorsal surface, 



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also called notum or scutum the former is the more com- 

 mon but less appropriate term, an under surface or ster- 

 num, and two lateral surfaces or pleura ; these parts, like 

 the legs, take their names from the segment to which they 

 belong, and those segments only which bear the legs are 

 usually examined for distinctive characters : the prothorax 

 has a pronotum, prosternum, and two propleura: the 

 mesothorax has a mesonotum, mesosternum, and two meso- 

 pleura: and the metathorax has a metanotum, meta- 

 sternum, and two metapleura : the propodeon has only a 

 dorsal surface in Hymenoptera, Coleoptera, and Orthoptera, 

 and therefore the simple term propodeon always designates 

 the upper surface, and no more particular description can 

 be needed. 



The notum and sternum are usually much more pro- 

 minent than the pleura ; they are also of much more solid 

 substance, so that in the contraction of the body incident 

 on emptiness, and on drying after death, these harder por- 

 tions, especially of the abdominal segments, remain ex- 

 tended and prominent, while the lesser and softer portions 

 constituting the pleura shrink and become invisible ; in- 

 deed if we look at the abdominal segments of a wasp or 

 a Sphex (see the fig. at page 145), we shall find the dorsal 

 and sternal portions completely wrapping round the insect, 

 and these portions alone possess any characters by which 



