106 ON THE ANATOMY OF THE FLY. 



regarded as the dorsal lateral appendages, as they are continuous with the 

 plate itself as well as with the lateral rods. But the ventral plate of this 

 segment is deeply notched on either side behind, and a pair of curved hollow 

 nipple-like organs, each bearing several setee, are articulated with these 

 notches; they evidently represent the inferior lateral appendages and 

 probably curve over the leaf -like organs on the dorsal aspect of the 

 ovipositor. The dorsal prolongations of this segment act as springs ; when 

 at rest they are directed forward, and lie with their broad surface in a 

 horizontal position ; when the segments are partially protruded, they are 

 turned back with their broad edges directed vertically ; this is effected by 

 muscular action through the medium of the lateral rods. 



The remainder of the sexual apparatus consists of a single segment. 

 The internal valve-like pieces which surround the rectum are probably its 

 dorsal lateral appendages ; this will appear more likely by comparing 

 them with their homologues in the female which are separated by a small 

 triangular dorsal plate. (Plate X., fig. 5.) 



The intromittent organ (Plate IX., fig. 10) probably represents the ventral 

 lateral appendages of the same segment, fused more or less into one. It 

 presents perfect lateral symmetry, and is supported by a hinge- joint upon 

 a very large apode"me (Plate IX., fig. 11) ; each lateral half is articulated 

 separately with this apod6me, and each bears at its base a palpus-like 

 organ articulated with it by a distinct ginglymus joint. The two lateral 

 halves are united by a curved spine or crest, which arches over the ejacu- 

 latory duct. 



Each lateral half consists of a slightly curved hard rod of chitine, broad 

 at its base, but gradually becoming thin towards its extremity, which is 

 terminated by a small triangular knob. About half way between the base 

 and apex of each of these rods on its under side is a proj ecting process 

 which bears a curved plate, serrated along its inferior border, and uniting 

 with its fellow in the mesial line. These plates terminate in pointed pro- 

 cesses at their outer posterior angle, but their middle portion is continued 

 backward, and turns up to surround the ejaculatory duct, which lies upon the 

 upper surface of these plates except at their posterior extremity, where 

 they form a complete tube, united anteriorly with the duct, and opening 

 posteriorly in a broad trumpet-shaped mouth. (Plate IX., fig. 12.) 



The intromittent organ is moved by a mass of muscles arising from the 

 handle-like apod&ne which supports'it ; these are inserted into the lateral 

 halves of the organ as well as into the bases of its palpus-like appendages 

 other muscles arise from the eighth ventral plate, and are inserted into 

 the apode"me. 



Unless the apodSme represents the ventral plate of the ninth segment, 



