BRISTLES: THEIR IMPORTANCE IN IDENTIFICATION 445 



parts, one vertical and the other horizontal, united together to form the 

 'boomerang rod' (cp. Plate LV, figs. 3 and 6). The vertical portion 

 is internal, and is concealed by the eighth sternite, while the horizontal 

 part, also mainly concealed, projects distally from the end of the 

 abdomen, and bears a few hairs. In many preparations, and in the one 

 from which figure 1, Plate LI 1 1, was made, the vertical portion of the 

 boomerang rod and the manubrium of the ninth tergite lie in the same 

 plane, and cannot be readily distinguished from one another. 



The terminal segments in the female (Plate LIII, fig. 2) are somewhat 

 compressed. The eighth tergite is narrow in the dorsal line, but expands 

 laterally and extends almost to the ventral line, thus 

 occupying almost the whole of the lateral area of the ' * * 



terminal part of the abdomen. The eighth sternite is 

 correspondingly reduced, and forms an inconspicuous plate below the 

 tergite. The ninth tergite bears the pygidium as in the male, and is 

 comparatively small. Immediately below it there is a small conical 

 projection, bearing a tuft of hairs, known as the stylet (Plate LIII, 

 fig. 5 ) ; this and the small plate posterior to the pygidium from which it 

 arises comprise the tergite of the tenth segment. The ninth sternite is 

 almost entirely concealed by the eighth tergite and is of an irregular 

 shape ; the tenth sternite, bounding the anus below, forms a small projec- 

 tion below the stylet. The genital opening lies between the ninth and 

 tenth sternites. 



With the exception of the form of the clasper the parts in C. felis 

 conform to the general type found in the Pulicidae. The differences are 

 not so great as to render the parts unrecognizable, if care is taken to 

 mount the dissections in a natural attitude. 



The spiracles of the flea are regularly arranged. There are three in 

 the thorax, in the positions indicated in the figure, and one between each 



of the abdominal segments from the second to the 



Spiracles 



ninth. They lie in the soft portion of the tergite, 

 above the middle line of the lateral surface. That of the first abdominal 

 segment lies between the tergite and the epimerum of the metathorax. 

 The spiracular openings are enclosed by rings of chitin, and are easily 

 recognized in cleared preparations. 



The arrangement of the hairs or bristles on the integument of C. 

 felis is sufficiently indicated in the figure. It will be seen that they 

 are for the most part arranged in regular rows, one The vegtiture 

 to each segment, and that the rows are not placed 

 terminally, but in the middle of the chitinous plate, where the chitin 



