1909.] natural sciences of philadelphia. 5 



Terminology. 



The modern terminology for the thoracic sclerites is based upon the 

 epoch-making work of Audouin, '20. Discarding the then prevalent 

 conception of a binary division of the thorax according to the function 

 ©f its organs of locomotion (as, for example, the collum and pectus of 

 Knoch, 1801, the corselet and segment alifere of Chabrier, '20, or the 

 mani- and ali-truncus of Kirby, '28) this author demonstrated that 

 the thorax is composed of three similar segments. These three he 

 designated as the pro-, meso-, and meta-thorax — terms variously 

 attributed to Kirby, Latreille and Audouin, but which appear to have 

 been first proposed by Nitzsch, '18. Nitzsch, however, used the 

 slightly different form protothorax instead of prothorax. 



Each segment Audouin considered as composed of four regions, 

 namely, a dorsal region or tergum, two flanks or "pleurae," and a 

 ventral region called the sternum. The sternum he regarded as con- 

 sisting of a single piece, but for the flanks and tergum he described a 

 number of subdivisions. 



In the flank or "pleura," he recognized the following parts: two 

 large lateral plates, the anterior of which he termed the episternum, 

 and the posterior the epimeron; a narrow strip along the anterior 

 margin of the episternum called the parapleuron ; a small plate con- 

 taining the spiracle, called the peritreme; and a triangular sclerite 

 articulating with the coxa, called the trochantine. 



The tergum he considered as composed of four regions, lying one 

 behind the other. Beginning with the most anterior he termed these 

 the prsescutum, scutum, scutellum and postscutellum. 



Some entomologists employ the word dorsum to designate the tergal 

 region of a single segment, but it is far preferable, as Audouin has 

 done, to apply this term to the whole dorsal surface of the insect. 



The expression stigma is frequently used as synonymous with spir- 

 acle, especially in the German publications; but, as used by system- 

 atists, the word stigma denotes the chitinized cell in the costal region 

 of the wings of certain Hymenoptera, etc. It would, therefore, be 

 preferable to use only the more exact and suitable term spiracle to 

 denote the tracheal opening. 



In most of the modern works there is a very great laxity in the use 

 of the singular and the plural form of the word pleura. For example, 

 some authors speak of one flank as the pleuron and both together as 

 the pleura, while others, following Audouin's example, choose the 

 latinized forms pleura and pleurae. One cannot employ the term 

 pleura in both a singular and plural sense without creating confusion, 



