444 MEDICAL ENTOMOLOGY 



The remaining segments differ in the two sexes. They are of the great- 

 est importance from the point of view of classification and identification 



of species, as they present great variety of form, and 

 External genitalia ,. , , , 



provide reliable taxonomic characters. The parts can 



only be examined satisfactorily by dissection, after preliminary macera- 

 tion in potash ; specimens should be mounted both in profile and flattened 

 out, and in the case of the female in such a way as to permit of exami- 

 nation from the posterior aspect. 



The most important of the terminal segments in the male is the ninth, 

 which is of a most complex description ; part of it is visible externally, 

 and part concealed beneath the segments anterior to it. At the posterior 

 end of the abdomen, projecting upwards and backwards in a conspicuous 

 manner, there is a pair of large oval plates (Plate LI 1 1, fig. 4), each 

 of which has a fringe of stout hairs around its periphery, and three or 

 four longer bristles on its external surface ; these are the daspers, a part 

 of the male accessory genital organs. Anterior to them, and occupying 

 the greater part of the dorsal portion of the segment, there is on each side 

 an oval plate termed the pygidium. The surface of this has on it a num- 

 ber of small clear areas, from each of which there projects a long and ex- 

 tremely fine hair. The space between and surrounding the clear spaces 

 is beset with a dense coat of fine recumbent hairs, which are heavily pig- 

 mented, rendering the whole pygidium a prominent object in cleared 

 preparations. The pygidium is evidently a sensory structure ; it occurs 

 in all fleas, but its precise function is unknown. 



The dorso-lateral portion of the ninth tergite extends a little distance 

 posterior to the base of the clasper, and forms the distal extremity of the 

 abdomen in the upper part. Anteriorly a projecting flange passes from 

 its border underneath the eighth tergite. The ventral border of this 

 flange and the posterior border of the sclerite converge at the posterior 

 and ventral angle, and are here produced downwards and forwards into a 

 conspicuous rod (m. in Plate LI 1 1, fig. 4), which lies underneath the 

 eighth segment, extending as far forward as does the flange. This is the 

 manubrium, and to it are attached the muscles actuating the claspers. 



The form of the ninth segment in the male Ctenocephalns felis is not 

 very typical of the Pulicidae. The clasper is usually divided into several 

 portions, as in Pulex irritans (Plate LV, fig. 6). The clasper is fre- 

 quently spoken of as the ' moveable finger '. 



The tenth tergite is entirely internal, and is probably mainly absorbed 

 into the complex penis sheath. 



The ninth sternite has a characteristic shape. It consists of two 



