STRIDULATING OEGAN IN A SOUTH AFRICAN ANT. 273 



being then reflected from the narrow upper edges of the teeth 

 alone ; but if the light is allowed to fall upon them from the 

 opposite direction (Fig. 6) it is reflected from the concave 

 anterior surface of each, giving them the appearance of so many 

 elongated oval patches shining like mirrors upon the dark back- 

 ground in which they are set. 



This stridulating band is firmly fused by its posterior margin 

 to the succeeding ventral abdominal segment, but it is free to 

 slide within the segment which precedes it, so that when the 

 extremity of the abdomen is curled under and forward, the band 

 is entirely overlapped and the edges of the 1st and 3rd segments 

 (as reckoned from the stalk) are approximately in contact. 

 The preceding segment is very large and rigid and is formed 

 of extremely hard chitine, but its posterior margin is readily 

 seen to be incurved and to be reduced in thickness to a knife- 

 like edge, which presses in gentle contact upon the stridulating 

 band. The action of the whole apparatus will now be obvious 

 (Fig. 5); as the apex of the abdomen is depressed and curled 

 the band slides under the knife edge referred to, which passes 

 easily over the inclined faces of the rows of teeth, but when the 

 abdomen is extended again with a sudden jerk, the teeth pass 

 under the hard incurved edge in the opposite direction, striking 

 the perpendicular face of each against it and causing it to 

 spring down with some force upon each row in rapid succession, 

 each such jerk of the abdomen being thus necessarily accom- 

 panied by a very perceptible chirp or squeak, the pitch of which 

 will depend upon the rate at which the resulting vibrations 

 succeed each other. 



Stridulation in ants is not at all new, having frequently 

 engaged the attention of entomologists and been made the 

 subject of many communications to Societies at home and 

 abroad. A paper by Dr. David Sharp read before the Entomo- 

 logical Society in June, 1893, and published in their Proceed- 

 ings, describes these organs in about 20 species belonging to 

 four genera, of which two at least are British. Figures are also 

 given, but there is nothing amongst these which corresponds to 

 the one which is the subject of the present paper, and Dr. Sharp, 

 to whom 1 submitted some drawings, informed me that he had 

 not yet seen one like it. 



The specimen exhibited under the microscope in the room 



