21 



Duthiers, thus making the eleven; but the incisions marking these folds are 

 incomplete, not reaching the lower margin of the plate. Between the second 

 of these folds and the terminal piece on each side issues a short process, not 

 extending beyond the apex of this piece ; these appendages are the cerci 

 (Fig. 1, cr). 



Fischer* says the abdomen in both the male and female consists of nine 

 distinct segments. Westwoodf remarks that the inferior surface of the 

 abdomen in the male consists of eight segments, but only of seven iu the 

 female. Lacaze-Duthiers says the sub-genital plate is formed hj the seventh 

 sternite (ventral segment) ; yet, in his figure, PI. XII, Fig. 1, it is marked as 

 the eighth. If we consider the piece which projects forward into the 

 posterior margin of the metasternum (see PI , Fig. 8, the square piece in 

 the middle of the posterior margin with an oblong projection forward), as 

 belonging to the venter, and as representing the first sternite, which I am 

 inclined to think it does, then there are eight ventral segments (sternites) in 

 the female and nine in the male. 



Each abdominal ring is, or is supposed to be, composed of six pieces 

 soldered together, three to each lateral half; but, for all the purposes of the 

 present work, we may consider them as composed of but two pieces or 

 plates — an upper or dorsal plate called the tergite or dorsal segment, and the 

 lower plate called the sternite or ventral segment. The under surface of the 

 abdomen as a whole is the venter. 



On each side of the basal segment is a large cavity, either of a serai- 

 orbicular or lunar shape, which is closed on the inside by a very slender skin 

 of a whitish color. This is the tympanum, and is supjiosed by some ento- 

 mologists to have a certain influence upon the act of stridulation, while others 

 believe it to be the organ of hearing ; the latter appears to be the more 

 generally received opinion at present. 



The apex of the ventral portion in the males curves upward somewhat 

 in the form of the prow of a vessel ; this curved portion, in some species, 

 appears to form the last ventral segment (sternite), but in others a transverse 

 impression is seen separating the apical surface from the rest. This apical 

 portion has received several different names ; as, sub-genital lamina, sub-anal 

 plate (Fig. 2, sap'), &c. In some genera and species ( Tryxalis, Mesops, some 

 Opomala, &c.), the tip is entire ; while in others it is notched. 



* Ortliop. Europ., 286. tMod. Classf. Insec, I, 457. 



