OF WATERBUGS, ESPECIALLY OF CORIXIDAE. 37 



arranged in regular rows. These are the passive agents, the 

 " stridulatory area J' This area is diversely developed in v^arious 

 species, but is seen very distinctly in {e.g.) Corixa geoffroyi (Figs. 

 16 and 26), and C. striata. 



The stridulation, in my opinion, is performed as follows : — 

 The " comb " of the left tarsus is drawn somewhat obliquely 

 across the femur of the right leg, or vice versa. The fact that 

 the face of Corixa is at an acute angle to the dorsal part of the 

 head (the vertex), and its apical margin almost contiguous to 

 the base of the anterior femora, has probably misled observers. 

 The stridulatory area (as the femoral area may be termed), 

 occurs in a highly developed state only in the males, and is 

 present in the males of all the British species of Corixa, while 

 it is feebly developed or absent in every female of that genus. 

 In the closely allied genus Cymatia, there is no stridulatoi-y area, 

 nor is there a corresponding tarsal stridulator in either sex. In 

 Micronecta I have not had sufficient fresh or alcoholic material 

 for satisfactory investigation, but there does not appear to be 

 any stridulatory area, and there are only bristly hairs on the 

 tarsus. In the males of Cymatia and Micronecta, the anterior 

 tarsus is terminated by a remarkably formed claw (Figs. 5 

 and 6). Handlirsch thinks that this may form some part of 

 the musical instrument. 



I feel assured that the principal method of stridulation in 

 Corixa geoffroyi is that which I have just described, but there may 

 well be other ways of producing recognisable sounds. The whole 

 surface of a Corixa is so minutely and delicately sculptured and 

 engraved, and the number and shape of chitinous bristles, pegs 

 and spines scattered regularly and irregularly all over the body 

 is so extraordinary, that one hesitates to pronounce positively 

 on their value in this direction. It is quite conceivable that the 

 long bristles on the palae in both sexes are employed to clean the 

 strongly carinate face, or the "rastrated" * surface of the pronotum 

 and elytra which obtains in many species, although the bristles 

 are as well developed in the smooth -surfaced C. geoffroyi as in the 

 deeply rastrated C. sahlhergi. 



The evolution of the palar " stridulators " is not difficult to 

 understand. A primitive form is found in Micronecta, where 



* Striated like a file. 



