( .-,3.1 ) 



f. 20 shows the mesosteruuni when viewed from ii ventral positioii. This has 

 the form of a very narrow iialf-ring. In the mesosternum there are no lines of 

 division externallv visible ; the various pleural or ventral jiieces are fused together, 

 the two portions shown in f. 2n heinjr thi' mesosternum and the cpimeron 

 (mst + cpm). 



■\Vhen viewed from the front (I'l. X\li. f. '.':!) the mesosternum has the 

 appearance of a transverse plate which is not produced ventrally in the middle, 

 there being no intercoxal process. Indications of a division of the plate are visible 

 at both the lower and ujiper edges. 



The metasternnm is also narrow when viewed from a ventral position, but is 

 much longer than the mesosterunm. PI. XVII. f 20 demonstrates tiie fact that 

 the sternum forms a mesial tubercle and is well separated from the epimeron (epm). 



In f. 'i\, which represents the metasternnm in side view, tlie sternum is shown 

 ventrally produced into an intercoxal triangular tubercle. The tigure further shows 

 the position of the epimeron (epm) and the episternum fepst). The episternum is 

 a small piece lateral in position widely separated by the epimeron and sternum from 

 the coxal cavities. 



In a frontal view (f. 22) the epimeron, which lies behind the sternum, is not 

 visible ; the episternum, however, is plainly visible between the metasternnm and 

 the metanotnm. 



The three plates of the metathorax shown in PI. XVI. f. Ti, the side view ot 

 Cerntopsj/llii cloiiijutiin. 1 have termed' in the ])resent pa]ier sternum, episternum. 

 and epimeron. The homology of these parts as accepted by me has hitherto not 

 been recognized by others. I consequently give my reasons for introducing this 

 somewhat new departure. The genus ('eratopsyUn perhaps shows the plates in 

 qnestion best. In the accom])anying diagrammatic.il tigure of the metathorax of 



FlO. I. 



' '. cloiiijiitUK, the above-mentioned three plates are representeil. These in fact arc 

 present in all onr fleas, and have always the same position. They vary, however, 

 in outline and in respect to the bristles they bear. The large plate (ejjmj, the 

 epimeron, bears the metathoracic stigma at its uj)))er edge. It was often considered 

 to be a rudimentary wing by the older authors. Dr. Landois * erroneonsly treated 

 it as the ventral plate of the first abdominal segment. Tlie imier surface of the 

 epimeron serves for the insertion of the coxal muscles. The second jilate (epst), 

 the episternum, does not seeiu to have been clearly recognized by others as a 

 separate plate of the metathorax, though it is certainly indicated in many of 

 Taschenberg's figures. The coxal cavity is formed l)y the metasternnm and the 



* Aiuilnmw (lis ffv7uleJlo/in, p. 8 (ISC16). 



