134 Transactions of the Royal Microscopical Society. 
lapping portions of the second and third abdominal segments) are 
marked with very fine concentric ridges, but so is the projecting 
thoracic collar, on which the head articulates ; and this collar, when 
scratched with the point of a needle, emits the proper sound.” 
Landois, after referring to this opinion, expresses himself strongly 
in opposition to it. The true organ of sound is, he maintains,* a 
triangular field on the upper surface of the fourth abdominal ring, 
which is finely ribbed, and which, when rubbed, emits a stridulating 
sound. It certainly would appear, from Landois’ observations, that 
this structure does produce sound, whether or not we consider that 
the friction of the collar against the mesothorax may also assist in 
doing so. 
Under these circumstances, Landois asked himself whether other 
genera allied to Mutilla might not possess a similar organ, and also 
have the power of producing sound. He first examined the genus 
Ponera, which, in the structure of its abdomen, nearly resembles 
Mutilla, and here also he found a fully developed stridulating 
apparatus. 
He then turned to the true ants, and here also he found a 
similar rasp-like organ in the same situation. It is indeed true that 
ants produce no sounds which are audible by us ; still, when we find 
that certain allied insects do produce sounds appreciable to us by 
rubbing the abdominal segments one over the other ; and when we 
find, in smaller species, an entirely similar structure, it certainly 
seems not unreasonable to conclude that these latter also do produce 
sounds, even though we cannot hear them. Landois describes the 
structure in the workers of Lasius fuliginosus as having 20 ribs 
in a breadth of 0T3 of a millimeter. He gives no figure, however. 
Plate CXCII., Fig .2, represents the junction of the second and third 
abdominal segments in Lasius flavus, x 225, as shown by a longi- 
tudinal and vertical section. There are about ten well-marked 
ribs (r), occupying a length of about r Jo of an inch. Similar 
ridges also occur between the following segments. 
In connection with the sense of hearing there is another very 
interesting structure to which I must now call your attention. In 
the year 1844, Yon Siebold described! a remarkable organ which 
he had discovered in the tibiae of the front legs of Gryllus, and 
which he considered to serve for the purpose of hearing. These 
organs have been also studied by Burmeister, Brunner, Hensen, 
Ley dig, and others, and have recently been the subject of a mono- 
graph by Dr. Y. Graber,j who commences his memoir by observing 
that they are organs of an entirely unique character, and that 
* Loc. cit., p. 132. 
t ‘ Uber das Stimm. und Gehororgan der Orthopteren.’ Wiegmann’s Art. f. 
Natur., 1844. 
t ‘Die Tvmpanalen Sinnes apparate der Orthopteren.’ Yon Dr. Vitus 
Graber, 1875. 
