234 Professor Edward B. Poulton on the 
exercised with direct reference to females, or in rivalry 
to other males in the presence of a female. In the case 
of Psophus stridulus, true stridulation was only observed 
when the close proximity of a female had evidently 
thrown the male into a state of excitement. 
The following considerations also support the same 
conclusions. In Pezotettix pedestris, both sexes have 
rudimentary wings and the male never makes any audible 
sound. Nevertheless, when he is seated on the back of 
the female attempting to pair, and during coitus itself, 
he continually moves his third legs alternately as if 
in stridulation. 1 believe that this movement is a vestige 
of an ancient and long-lost power of producing sound. 
Although stridulation is usually produced by a symmetrical 
movement of the third legs, it will be shown that this is 
not the case with Stenobothrus elegans. ‘There is there- 
fore no objection to be raised against this character of 
the movement in Pezotettiz. Another view, and that 
held by my friend, the learned Orthopterist, Henri de 
Saussure, is that sound is really produced, only we cannot 
hear it. He holds that the sound is merely the outward 
expression of the elated feelings of the male Pezotettiz. 
Dr. Sharp, too, considers from the presence in 
apparently dumb species of well-developed tympana— 
and this is their condition in Pezotettic—<that the 
Orthoptera provided with acoustic organs, and which we 
consider dumb, are not really so, but produce sounds we 
cannot hear, and do so in some manner unknown to us”’ 
(Cambridge Natural History, Vol. v., 287). On the 
other hand, it may be urged that the perception of vibra- 
tion by means of tympana may be of great value in the 
life of an organism, even if the organism were incapable 
of producing sounds, and that it may be retained for 
some more general use when its original special function 
has ceased to exist. 
But in any case this movement of Pezotettix is con- 
ducted with an apparatus homologous with that by which 
sound is produced in other Acridiide, and yet one in 
which the special sound-producing structures are absent. 
The tegmina are too short to be brought into their usual 
relation with the femora, and the ridge on the inner face 
of the latter is without the “musical beads,” although 
strongly chitinized and prominent as though it had pre- 
viously possessed significance in this respect. 
