THE ABDOMEN 443 



anterior angle of the mesonotum. The portion behind this ridge is 

 regarded as the epimerum ; that in front of it is again divided into 

 two parts by a second ridge arising in common with the first, but passing 

 more obliquely forwards. The middle portion thus cut off, triangular in 

 shape in this species, is the episternum, while the lobe in front of the 

 suture, which is free on all sides except the posterior, is the sternum. 

 The latter forms a conspicuous projection between the first and second 

 pair of legs. 



The ventro-lateral plate of the metathorax is of considerably greater 

 extent, and passes backwards over the side wall of the . abdomen for a 

 considerable distance below the first abdominal tergite. It is divided 

 into two by a vertical ridge, commencing at the level of the insertion of 

 the coxa of the hind leg and continuous with the line of separation 

 between the metanotum and the first abdominal tergite. The part 

 anterior to the ridge is again divided into two portions by a horizontal 

 ridge, the upper portion being the episternum, and the lower, which is 

 much the larger, and which is continuous with its fellow of the 

 other side by a softer portion of chitin, the sternum. The portion 

 posterior to the vertical suture is the epimerum ; it extends behind 

 the metanotum and below the . first abdominal tergite, and is the 

 largest plate in the lateral wall. The epimerum is situated at the 

 widest, part of the body .of the flea, and forms the base of the abdomen. 

 The great development of this plate is, according to Jordan and 

 Rothschild, a special feature of the Siphonaptera. It replaces the 

 first abdominal sternite. 



In the abdomen the sclerites are more regularly arranged than in the 

 thorax. There are ten pairs in all, and of these the last three are 

 specially modified for sexual purposes. The first abdom- 

 inal tergite is broadest in the antero-posterior direc- The a b j en ( plate 

 tion ; it extends downwards on the lateral wall for only 

 a short distance, : and overlaps the epimerum of the metathorax,. The 

 sternite of the first abdominal segment is wanting. The plates of the 

 second to the seventh segments are simple arched bands, diminishing in 

 extent from before backwards in accordance with the shape of the body. 

 The second sternite lies behind the epimerum and is overlapped by it. 

 The dorsal plates are longer than the ventral ones, which they overlap. 

 The eighth tergite and sternite are smaller than the rest, and the tergite 

 is frequently telescoped inside the one in front of it, and is consequently 

 only seen when the parts are dissected out. It becomes visible when the 

 abdomen of. the flea is distended. . 



