OF THE SKELETON. 147 



we can distinguish insects from each other in our technical 

 descriptions. 



The notum or dorsal portion of each segment is occa- 

 sionally transversely divided by sutural lines or indentations 

 into four smaller portions or sections, and in the pro- meso- 

 and metathorax it is convenient to suppose all of these 

 sections present, although no division is distinctly dis- 

 cernable : the sections are called prcescutum, scutum, scu- 

 tellum, and postscutellum ; and entomologists agree in 

 calling a certain part the scutum of the mesoihorax in 

 Hymenoptera, and another part the scutellum of the meso- 

 ihorax in Coleoptera, without being able to trace in all in- 

 stances the existence of the other three component sections. 

 In the locust, as will be seen by a reference to the figure, 

 page 144, the prothorax is very distinctly divided into four 

 sections ; C 1 is the prcescutum, and immediately adjoins 

 the head ; C 2 the scutum ; C 3 the scutellum ; and C 4 the 

 postscutullem, adjoining the mesoihorax ; and this order 

 of nomenclature is preserved throughout the other seg- 

 ments, the prcescutum being invariably nearest the head, 

 and the postscutellum farthest from the head. In beetles 

 there is rarely any trace of sectional division in the pro- 

 thorax ; the dorsal portion would therefore be correctly 

 described as the pronotum, but the term prothorax is fre- 

 quently used and is universally understood, which after all is 

 the great object to be aimed at in anatomical nomenclature. 



In Hymenoptera the pronotum, mesonotum, and meta- 

 notum, are commonly each divided into two observable 

 parts, and these may be termed the scutum and scutellum 

 of each segment : in the Sphex, figured at page 145, the 

 unshaded segment C is divided very evidently into two ; 

 the anterior part resembles a neck, and is the pro thoracic 

 scutum, the posterior part more elevated and immediately 

 behind it, is the prothoracic scutellum. The next segment 



L2 



