PowELt.—On Stridulating Organs of Cicada. 287 
consisting of two cavities covered by scales. Hence the sound may truly be 
called a voice. In the female the musical apparatus is present, but very much 
less developed than in the male, and is never used for producing sound.” 
As I have not access to Landois’ original paper I am, of course, ignorant 
of the details of his description, but unless the cicada which he describes 
differs essentially in the nature of its musical organs from those found in New 
Zealand, and also from those described more or less correctly by other authors, 
especially Reaumur (see Kirby and Spence’s “ Introduction,” p. 501, seventh 
edition, 1856), he is most certainly in error. 
The stridulating organs of the cicada (Pl. XVIII.) are constructed on a prin- 
ciple which is, I believe, unique. In no other animal, as far as I am aware, are 
vibrating membranes made use of for the purpose of producing sound, and in 
this respect they possess a peculiar interest. In the male cicada on the upper 
surface of the first ring of the abdomen on either side may be seen a semilunar 
opening with convexity posterior, and on examining this opening with a 
magnifying glass it will be seen to lead into a shallow cavity closed in by a 
plicated horny membrane. [If a live insect be caught and these membranes be 
observed during the act of stridulation they will be seen to be vibrating 
rapidly, synchronously with the beats of the shrill sound. On examining the 
under surface of the insect an oval plate will be observed immediately behind 
each posterior leg, of considerable size, and quite free except anteriorly. On 
snipping off these plates with a fine-pointed pair of scissors we expose on each 
side a large triangular opening, the apices opposed to one another, and but 
slightly separated ; each opening leads into a roof-shaped cavity of considerable 
extent. Anteriorly this cavity is closed in by a fragile but opaque membrane 
divided into two parts by a chelinous rib, the lower half is pure white and 
marked with parallel creases, the upper half is yellow and tougher looking ; 
posteriorly the cavity is closed by a large tense beautifully transparent 
membrane, it is very delicate and shines with iridescent colours ; it is marked 
dr in the illustration. If we now carefully cut the body through anteriorly 
to the membranes here described, and to the stridulating membranes, by a 
little careful dissection we shall expose the immediate agent of the production 
of the sound, and see two thick yellow bundles of muscle inserted below 
into the parietes of the abdomen at the junction of the cavitary membranes. 
These muscular bundles diverge like the letter V, a delicate aponeurosis is 
given off from each muscle, which seems to be lost on the rim of the 
transparent membrane ; the muscle itself ends in a round tendon which is 
inserted into the under surface of the stridulating membrane. This membrane 
is highly elastic, and the sound is prodiiced by the contraction of the muscle 
straightening out the plications of the membrane ; this produces a click, and, 
on the muscle relaxing, the membrane from its elasticity springs back with 
he 
