THE INTEGUMENT OF THE THORAX. 03 



thoracic opening, and that of the meta-thorax is invisible exter- 

 nally, except when the abdomen is very much depressed, being 

 hidden under the post-scutellum of the meso-thorax. 



The pro-sternum or sternum of the pro-thorax (Plate V, Figs. 1, 7, and 

 8,) is situated immediately behind the cephalo-sternum. It consists of a 

 central portion and two cornua, which partially surround the anterior 

 coxae. The central portion is a long narrow plate, widest anteriorly ; it is 

 grooved along the mesial line externally, and presents a slight ridge 

 internally ; posteriorly, it sends a narrow plate along the edge of the 

 meso-sternum, and between it and the posterior edges of the coxae on 

 either side. This plate becomes broader externally to the coxa, and ex- 

 tends along the outer edge of its articulation, reaching the lower anterior 

 margin of the anterior spiracle, where it unites with the lateral plate of 

 the pro-thorax and terminates in a curved point in front of the articula- 

 tion of the coxa, near its outer anterior angle, behind the condyle. A 

 stout tooth springs from the outer margin of the aperture, near the an- 

 terior part of the opening, with which the coxa articulates ; it is hard 

 and polished, fits into a hollow on the outer side of the coxa, and forms a 

 point d'appui, upon which the leg moves. 



The posterior extremity of the sternum internally bears a pair of 

 processes, which are directed outwards upwards and forwards, and reach 

 the lower margin of the anterior thoracic spiracles, where they bifurcate 

 to surround those openings. I think it extremely probable that these 

 processes are part of an undeveloped segment intermediate between the 

 pro-thorax and meso-thorax. 



The meso-sternum (Plate V, Figs. 2, 5 a, 7, and 8 a,) forms the greater 

 part of the under surface of the thorax as well as part of the flank. It is 

 marked interiorly by a groove in the mesial line, and is deeply notched 

 posteriorly for the intermediate coxse. It bears very important internal 

 processes; one, the ento-thorax of the meso-sternum, extends its whole 

 length in the mesial line, and supports the great thoracic ganglion. 

 This is Y-shaped when seen either in front or behind, but presents 

 a large surface above, which lodges the ganglion ; its lateral 

 margins give insertion to muscles. Numerous muscles arise from nnd 



Fig. 13, The rod borne by the ampulla, the free extremity of which 

 fits into a concavity in front of the wing pivot. X 50 diam. 



Fig. 14, The wing socket. X 50 diam. 



Fig. 15, The valve, or epitreme, and peritreme of the meta-thoracic 

 spiracle. X 25 diam. 



Fig. 16. The valve, or epitreme, of the anterior thoracic spiracle, 

 X 15 diam, 



Fig. 17. The t>eritreme of the anterior thoracic spiracle, x 15 A' am. 



