38 G. -SV. KIRKALDY ON THE STRIDULATING ORGANS 



there are only short chitinous bristles (Fig. 6), scarcely differ- 

 entiated from the other rows. Is Micronecta able to produce a 

 sound vdih these comparatively soft, yielding bristles on the face 

 or elsewhere, or does the strong apical claw come into play? In 

 Cymatia (Fig. 5), a somewhat more primitive form of pala is seen 

 It is not known whether this genus stridulates. In Corixa 

 cavifrons, a form of pala somewhat intermediate betw^een Cymatia 

 and other Corixas is found. The stridulator is also in a state of 

 transition : the apical '• pegs " being scarcely distinguishable from 

 the bristles of Jlicroiiecta, while the basal ones are formed more 

 as in the typical species* (Fig. 9). 



Yet another suspected musical area is present, situated, at 

 least as regards one of the components, on the abdomen. In the 

 three genera discussed, the sexes are always very easily dis- 

 tinguished apart. Besides the shape and structure of the anterior 

 legs,t the segments of the abdomen are very diflferently formed, 

 both dorsally and ventrally. In the staid and conservative 

 females these are regular and subparallel. In the males 

 they are irregular, split and disordered (Fig. 34). On the upper 

 surface, near the lateral margin of the sixth segment, is a remark- 

 able organ, present only in the males of certain species of Corixa 

 and Micj'OJiecta, discovered in 1873 by F. B. White {6a). It 

 consists of a (variously shaped, according to the species) slightly 

 convex, chitinous plate, attached to the abdominal segment by a 

 short cliitinous, apparently structureless, pedicle. This plate is 

 formed of from 3 to 1 6 (according to species) rows of very closely 

 set teeth — strongly resembling the teeth of a comb; the rows 

 overlap more or less, and are very irregular in some species. This 

 organ, which is situated on the left side of the abdomen in the 

 typical subgenus of Coi'ixa {geoffroyi and affinis), and on the right 

 side in the other subgenera which possess it, was termed the 

 " strigil," or " curry-comb " by its discoverer, and is considered by 

 Handlirsch to be a stridulating organ. It does not seem possible 

 that it could be employed under water — the only occasion when 

 the sounds have been heard — as under these circumstances the 



* The "pegs" vary in shape very considerably in the various species, 

 but for examination a comparatively high power, such as "Zeiss F, is 

 necessary, and I have not had sufficient leisure for this. 



t In the males of CorLva and Cymatia, the face is more or less deeply 

 excavated, while in the females it is either flattened {Corixa carifrons and 

 Cymatia) or convex. In Micronecta the face is convex in both sexes. 



