EXTERNAL GENITALIA : GLOSSINA 87 



when the specimen is mounted dorsum uppermost. The intermediate 

 appendages arise from the base of the first joint of the superior clasper, 

 and occupy a median position, surrounding the penis. The intromittent 

 organ is the central part of the whole apparatus, and contains the duct 

 from the internal reproductive organs. It is a thin rod-like structure, 

 highly chitinized, and has at the upper end a small oval chitinous 

 swelling, at the lower end of which it receives the ejaculatory duct ; at 

 the distal end it terminates in a barbed chitinous penis. The swell- 

 ing at the upper end of this organ contains much delicate muscle 

 fibre, and is said to function as a pump to regulate the exit of the 

 spermatozoa. 



In the Orthorraphic flies it is usual to find the external genitalia 

 strictly external, and some parts of them, usually the superior claspers, 

 visible without dissection, as in Phlebototnus. In the Culicidae the 

 superior claspers (Plate XVIII, fig. 6) are easily seen in mounted prepa- 

 rations, and their shape and the angle at which they are attached to 

 the abdomen are used as characters in classification. In Tipula and 

 Asilus the male genital armature is very conspicuous, and also of a very 

 complex description. In Tabanus (Plate XVIII, fig. 5) the claspers are 

 withdrawn beneath the terminal tergite, and can only be seen when 

 dissected out. In the Cyclorraphic flies the parts are always concealed 

 within the end of the abdomen, and can only be examined in specially 

 made preparations. In Musca and its near allies the parts usually have 

 a sinistral asymetry, and are composed of a complex of chitinous plates 

 which have been differentiated as tergites and sternites of suppressed 

 segments of the abdominal wall. The complexity of the parts is so great 

 that it would serve no purpose to give a detailed description of them 

 here. Those of Glossina, however, are of importance in classification, 

 and demand further consideration. 



The ventral aspect of the end of the abdomen in Glossina has on it a 

 convex oval swelling, with a groove down the middle line. When the 

 part is cleared in potash and dissected, it is found 



that the area of this swelling is formed by a separate External Genitalia 



. ... ,.,.-, i ,- of Glossina 



plate of chitm, which is articulated by its posterior 



end to the ventral plate of the eighth segment of the abdomen, and is 

 free for the rest of its periphery, so that it can be folded downwards 

 and backwards until it projects at the distal end of the fly. The 

 hypopygium as seen externally is in fact only the outer casing, the 

 functional parts being concealed on its internal surface, and only 

 displayed when the plate is everted. They consist of the following 



