COCKROACHES, ETC. 141 



Hierodula gastrica, showing the dentate edge with a 

 small seta springing from the side of each tooth. 



Stridulation, though almost the rule rather than the 

 exception among the saltatorial Orthoptera, is certainly 

 exceptional amongst the non-saltatorial families. Most 

 of the Mantidce cannot produce a hissing noise, but 

 only a rustling noise, "which, since it is caused merely by 

 the sudden opening and closing of the fan-like wings, 

 does not come under the head of stridulation at all. 

 Two African Cockroaches belonging to the genus 

 Nauphceta possess the power of stridulating when 

 alarmed or irritated, and in the case of one of them 

 the noise made is a loud chirp, which can be heard 

 to a distance of several yards. 1 It is produced by 

 rubbing the edge of the wing-cover at the shoulder 

 against the under-side of the prothoracic shield. The 

 edge of the wing-cover is armed with rows of minute 

 asperities, 400 to the millimetre, specialized develop- 

 ments of the polygonal fields into which the chitin 

 of the wing-covers is split up, showing that it was 

 developed from cells. The under side of the pronotum 

 at the edge against which the wing-cover file is brought 

 to bear is transversely ridged. Since this apparatus is 

 possessed by both sexes, it is probable that the 

 stridulation is a warning signal, as it is in the Mantida, 

 and not a love song, as in the saltatorial Orthoptera. 

 Stridulation in the Phasmidce will be discussed when 

 we come to treat of that family. 



I mentioned above that nearly all the Mantidce had 

 a very uncertain gait when walking, and that con- 

 sequently they could not run down their prey. The 



1 Vosseler, Deutsch. Ent. Zeitschr., 1907, p. 527. 



