364 
POPULAR SCIENCE REVIEW. 
Cicada. After having been excited by its motor muscle, the 
drum returns to its state of rest by virtue of its elasticity,* an 
effect aided by the chitinous bands. Some authors have stated 
that the drum becomes concave at the moment of the contrac- 
tion of the motor muscle, but the real fact is that, with the ex- 
ception of a very slight depression at the point of attachment 
of the tendon, the membrane constantly retains its convexity, 
and never yields, at all events, in adult insects. In young spe- 
cimens, however, the drum, having less power of resistance, is 
rendered somewhat concave by the action of the muscle, and this 
peculiarity was utilized by M. Carlet to demonstrate the syn- 
chronism in the vibration of the drums. For if these he exposed, 
by cutting the wings of a young specimen of (7. hcematodes , 
they will be seen, during the song, to be at one and the same 
time both concave or both convex. 
M. Sober, after carefully examining the muscle of the drum 
during song, was not, even by the aid of a lens, able to distin- 
guish the slightest movement ; but M. Carlet, on repeating the 
experiments, plainly observed a to-and-fro motion of the muscle, 
and concludes that M. Sober must have experimented on a 
Cicada already tired out. M. Carlet has further attempted to 
register the vibrations of the drum, and by the following 
method. A long needle of glass, drawn out to a thread in the 
flame of a spirit-lamp, was fixed at a tangent by means of a 
little wax to the exposed drum-membrane, and the insect, held by 
the end of its body, while in song, was made to trace the vibra- 
tions on smoked paper rolled round a cylinder rotating by clock- 
work, f simultaneously with tracings of a standard tuning-fork. 
By comparing the two sets of tracings thus obtained, the number 
of vibrations made in one second by the drum could be cal- 
culated. The numbers cannot be given by M. Carlet, because 
they are not constant. The captive Cicada, however, cries rather 
than sings, the musical sound being probably modified by the 
mutilation to which the insect is subjected, as well as the em- 
barrassment caused by the wax on the drum and the friction of 
the glass index against the smoked paper. It has been stated 
some pages further back that there is no tensor muscle of the 
drum, and that if there were one, it would be a hindrance 
rather than a help. The reason is this — that the membrane, 
* This is a good example of physiological economy. Similar instances 
may he found in the passive action of the costal cartilages in antagonism to 
the active contraction of the muscles which expand the chest in respiration, 
and in the elasticity of the hinge in passive opposition to the adductor 
muscle which closes the two valves of the shell in the oyster. 
t An apparatus probably resembling the well-known arrangement of 
Professor Marey. 
