36 G. W. KIRKALDY ON THE STRIDULATING ORGANS 



Corixidae) the rostrum is very short and obscurely jointed in both 

 sexes. It is strongly sculptured, having six parallel transverse 

 keels, and two closely approximated longitudinal median keels. 

 The apical margin is, according to Handlirsch, slightly roughened 

 in the male, and it is on this part that the Austrian author 

 believes the stridulation to be , effected by the anterior tarsi. It 

 is extremely difficult to observe accurately in the case of a minute 

 insect inhabiting water, and at the same time very shy of 

 observation, but I believe that I have observed the actual method 

 of nerformance. The sexual difference in the structure of the 

 rostrum is almost inappreciable to me, and moreover, the apex is 

 thickly covered by stout bristly hairs, probably forming an 

 effective bar against any overtures from the tarsi. 



Also, the tarsal "comb " show^s a remarkable degree of special 

 modification in the male sex quite out of proportion to the feeble 

 roughening of the supposed stridulatory area developed on the 

 rostrum.* 



The anterior pair of legs is extraordinarily modified in both 

 sexes (Figs. 1 and 7). The femora are considerably thickened (Figs. 

 la and 2), varyingly so according to the species, but almost always 

 more so in the male than in the female, often very much more ; 

 the tibiae are very short and thick (Fig. Ic), and the tarsi are 

 single-jointed, thickened, more or less knife- or spoon-shaped 

 (Figs. Id and 7d). In the females, the lower margin of thepcda (as 

 this thickened tarsus is called), is furnished with a number of long, 

 bristly hairs, and a curved line of very short hairs of a somewhat 

 similar texture runs across the interior surface. In the males, 

 there is a similar, slightly shorter, row of long bristles, while the 

 shorter row is noticeably longer than in the other sex. There is 

 also on the inner surface, nearer to the upper margin, a row, 

 varying in position, form, etc., according to the species (as does 

 also the exact shape of the pala), of small, elongate or rounded 

 chitinous " pegs " or " teeth," which Carpenter terms the " comb." 

 These are the active agents in the stridulation — the ^^ siridulator." 

 On the inner surface of the femora (in the males only), near 

 the base, is a specially modified area f of minute chitinous pegs, 



* Ilandlirsch's figure of the rostrum is a little diagrammatic, since the 

 internal edges of the two central keels are not really straight and con- 

 tiguous along their entire extent, as he shows them. 



f This area is also found in the female, but not nearly so highly modified. 



