6 PROCEEDINGS OF THE ACADEMY OF [Jan., 



and as the words are of Greek origin it would seem advisable to use 

 only the etymologically correct forms, pleuron and pleura. 



Recently the terms tergite, pleurite and sternite have been used 

 interchangeably with tergum, pleuron and sternum. One form of the 

 word appears to be amply sufficient for all ordinary purposes, and it 

 would be far more practical to use the term tergite for a subdivision 

 of the tergum, pleurite for a part of the pleuron, and sternite for a 

 sclerite of the sternum. Thus the prsescutum, scutum, etc., would 

 be tergites, the epimeron and episternum pleurites, and so on. It is 

 in this sense that these terms have been used in the text. 



Theoretical Discussion. 



Before taking up the subdivisions of the segments in detail, a brief 

 review of the theories dealing with the formation of the thorax will serve 

 to give a clearer idea of the nature of the sclerites. 



Despite Newport's, '39, statement to the contrary, Audouin seems 

 to have regarded the thorax as consisting of but three simple seg- 

 ments. MacLeay, '30, however, and after him Newport, '39, proposed 

 that each of the pro-, meso-, and meta-thoracic segments is in reality 

 composed of four subsegments or annuli, which have become more or 

 less completely fused together in the formation of the compact, highly 

 specialized thorax. The prsescutum, scutum, scutellum and post- 

 scutellum, according to this theory, are the tergal portions of the four 

 annuli, which are more closely fused in the pleural region and com- 

 pletely consolidated in the sternal region. 



Hagen, '89, on the other hand, holds the view that each segment is 

 composed not of four, but of three subsegments, each bearing a charac- 

 teristic appendage. The most anterior he terms the leg-bearing, the 

 next following the wing-bearing, and the last the spiracle-bearing 

 subsegment. 



The more modern theories are founded upon the work of Patten, 

 '90, who claims that the thoracic segments are composed of but two 

 annuli. From a comparison with the nervous system of Scolopendra, 

 which he takes as a type, he concludes that in all Anthropoda the 

 neuromeres, and consequently the segments themselves, are in reality 

 double. In support of this view, he states that "in all anthropods 

 carefully studied two cross commissures have been found in each 

 neuromere," thus indicating the double nature of these structures. 

 Furthermore, "in Acilius the median furrow between the cross com- 

 missures is similar to that found between the successive neuromeres." 

 "In Scorpio the neuromeres are distinctly double," and in such forms 



