360 POPULAR SCIENCE REVIEW. 
rest. The other abdominal segments, which help to make up 
the lower part of the framework of the musical organ, present 
nothing worthy of note, except that each has a stigma on the 
ventral surface. 
B. Vibrating Membranes. — The principal are the three fol- 
lowing : the drum (“timbale,”) the mirror (“ miroir, 5 ’) and the 
folded membrane (“ membrane plissee,”), and are all situated in 
pairs on either side of the median plane. 
1. The drum (“ timbale ” of Reaumur) (t, figs. 1,2, 3), some- 
times also termed “tympan,” is translucid, and is imbedded in a 
rim (“cadre,”) from which it projects into a hollow called the 
cavern. In coincidence with its rim the circumference is ellip- 
tical. Of its surfaces the outer one is convex ( t , fig. 2), and 
is furnished with five or six chitinous arches, while the inner 
surface is concave. At the hinder point of junction of the arches 
is a thickened spot where the tendon of the motor muscles of 
the drum is inserted (fig. 1). The membrane itself is composed 
of an epidermic tissue made up of lozenge-shaped cells. In 
females the drum is represented by a chitinous scale imbedded 
in a rudimentary tympanic rim. 
2. The mirror. — The membrane so named by Reaumur is 
stretched between the lower borders of the wing of the entogas- 
trium , the base of the internal surface of the tetrahedron and 
the ventral part of the first abdominal somite (mi, figs. 1, 2, 
3). It is in the form of a semicircle, of which the diameter is 
the internal edge of the wing of the entogastrium , (vide fig. 
1 ). It is a flat and diaphanous plate of extreme thinness, hav- 
ing in its middle iridescent rings. Microscopically it is made up 
of a layer of lozenge-shaped cells, like those of the drum, but 
much more delicate. The two mirrors are separated in the 
middle line by the body of the entogastrium (vide fig. 2). 
They are, lastly, rudimentary in the female insect. 
3. The folded membrane (“ membrane plissee,” m p, figs. 1, 
2, 3). — This organ is soft in the fresh state, and transversely 
folded in repose, whence the name given to it by Reaumur. By 
its laxity it differs from the drum and the mirror, which are 
always dry, ergo , more or less tense, membranes. It is, moreover, 
opaque, while the first named is translucid and the latter diapha- 
nous. It has the form of a rectangle, of which the two surfaces 
are directed anteriorly and posteriorly. The membrane * itself 
is composed of two layers, one superficial, of elastic fibres, the 
other deep, of the nature of a lining membrane. The elastic 
fibres lie parallel and are folded zigzag-wise. It is, like the pre- 
ceding organs, rudimentary in the female Cicada. 
C. The Muscles. — There are three pairs, of which only one 
has been previously described by naturalists. They are symme- 
trical, two and two, and are absent in the female. 
