178 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



The Paratreme {20) is seen best from the interior of the 

 thorax. It is a distinct and irregularly quadrate sclerite, 

 bounded above and internally by the prescutum and the pro- 

 phragma, below by the extremity of the prodorsal arch, and 

 externally by the spiracle, above which it just reaches the 

 lateral plate and the dorso-pleural syndesmosis. Although the 

 limits of the paratreme are not very readily seen externally, 

 they are marked by a very distinct sutural ridge projecting 

 into the thoracic cavity. 



The Epitrochlear Sclerite is a quadrangular vertical plate, 

 articulating with the paratreme and prodorsum above, and 

 with the condyle by its inner margin. 



Its external surface is convex, and projects in a tooth-like 

 process, overhanging the anterior coxa in front. 



The external edge of the epitrochlea is formed by the 

 descending process of the hypotreme. 



The Sclerites of the Prosternal Area are nine in number : the manubri\nn, 

 two pairs of clavicukc, anterior and posterior, and two pairs of pectoral 

 sclerites, the greater and lesser pectorals. 



In the immature imago these sclerites are all distinct chitinous thickenings 

 of the syndesmotic integument ; but in the mature insect the clavicuhc are 

 fused with the manubrium and the epitrochlear sclerites. 



The Claviculae. — The anterior clavicula is a thin rod of chitin, extending 

 from the anterior edge of the manubrium to the epitrochlea. The posterior 

 clavicula is somewhat shorter and broader, tapering at its extremities. 



The Great Pectoral is a triangular sclerite, which flanks the manubrium, 

 with its short edge adjacent to the clavicula. 



The Lesser Pectoral sclerite is a minute convex caudate fold between the 

 great pectoral and the anterior coxa. It is broadest behind, and is covered 

 with minute bristles. 



I'he clavicuhu unite with each other and with the pectorals in the adult 

 insect, and so complete the foramina with which the anterior cox;v articulate. 



The integument of the prosternal area is continuous with that of the 

 neck. 



The Neck is very narrow, sub-cylindrical, and covered by syndesmotic in- 

 tegument, in which seven sclerites are apparent. These are a median ventral 

 sclerite — the sella, to which allusion has already been made; a pair of acces- 

 sory pieces in front of the sella— the cornicula; ; and two pairs of lateral 

 sclerites : a large posterior pair — the condyles ; and a small anterior pair— 

 the epicondyles. There is no dorsal sclerite in the neck of the fly, although 

 two dorsal sclerites exist in the neck of the cockroach [41]. 



The Sella (Plate VIII., Fig. 3) is a saddle -shaped sclerite, with two 

 remarkable transparent lobes in front, which form the lateral and upper walls 



