272 DIVISION III. ARTICULATED ANIMALS.— CLASS IV. INSECTA. 
excepted) presents to us many species which is peculiar to it. It nevertheless 
appears that the females, and neuters of those which live in society, have a 
longer existence. Many individuals bred in the autumn conceal them- 
selyes during the rigors of winter, and reappear in the following spring.” 
M. Lacordaire, in his “Jntroduction @ l’Entomologic,” makes some 
interesting observations in regard to the eyes of insects. 
They are of two kinds, called compound eyes, or eyes composed of many 
lenses, united by their margins, and forming hexagonal fucettes; and simple 
eyes, or ocelli. The exterior of the eye is called the cornea, each facette 
being a cornea; but the facettes unite and form a common cornea; these 
‘facettes, however, vary in size even in the same eye. 
The facettes are the most numerous in the insects of the Beetle tribe, 
a beetle’s eye having twenty-five thousand and eight; and least in that of 
the Ant, whose eye has only fifty facettes. On the under side of each 
facette we find a body of gelatinous appearance, transparent, and usually 
conical, the base of which occupies the centre of the facette in such a man- 
ner as to leave around it a ring to receive the pigment. This body dimin- 
ishes in thickness towards its other extremity, and terminates in a point, 
where it joins a nervous filament, proceeding from the optic nerve. These 
cones, agreeing in number with the facettes, play the part of the crystalline, 
or lens, in the eyes of animals. They are straight and parallel with each 
other. A pigment fills all the spaces between the cones, between the ner- 
vous filaments, and covers the under side of each cornea, except at the 
centre. This pigment varies much in color. There are almost always two 
layers, of which the exterior one is the more brilliant. In truth, these eyes 
often sparkle with fire, like precious stones. 
Of the wings of insects I shall speak when describing the typical species 
of the Winged Insects, merely mentioning here one extraordinary character 
of them. The buzzing and humming sounds produced by winged insects are 
not, as might be supposed, vocal sounds. They result from sonorous un- 
dulations imparted to the air by the flapping of their wings. This may be 
rendered evident by observing that the noise always ceases when the insect 
alights on any object. The sirene has been ingeniously applied for the pur- 
pose of ascertaining the rate at which the wings of such creatures flap. 
The instrument being brought into unison with the sound produced by the 
insect, indicates, as in the case of any other musical sound, the rate of 
vibration. In this way it has been ascertained that the wings of a gnat flap 
at the rate of fifteen thousand times per second. The pitch of the note 
produced by this insect in the act of flying is, therefore, more than two 
octaves above the highest note of a seven-octaye piano-forte. 
Some curious researches have been lately made on the strength of insects. 
