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ARTICULATED ANIMALS, 
sorts : the simple eyes, which present themselves under the 
form of a very small lens, commonly three in number, and 
disposed triangularly on the summit of the head ; and the 
composite, or eyes with facets, whose surface is divided into 
an infinity of different lenses, called facets , and to each of 
which a thread of the optic nerve corresponds. These two 
sorts may be united, or separated, according to the genera. 
We do not yet know whether, when they exist simultane- 
ously, their functions are essentially different or not ; but in 
both vision is performed by means very different from those 
by which it is caused in the eye of the vertebrata . 
Other organs which appear in this division for the first 
time, and which are found in two of these classes, the Crus- 
tacea and the insects, namely, the antennae , are articulated 
filaments, infinitely diversified in form, often so even accord- 
ing to the sexes, attached to the head, appearing eminently 
adapted for the purposes of a delicate tact, and perhaps of 
some other species of sensation of which we have no idea, 
but which possibly may refer to the state of the atmosphere. 
These animals enjoy the sense of smell, and that of hear- 
ing. Some place the seat of the former in the antennae. 
Others, like M. Dumeril, at the orifices of the tracheae; 
others again, like M. Marcel de Serres, in the palpi. But 
these opinions are by no means founded on positive and 
conclusive facts. With regard to hearing, the decapod Crus- 
tacea, and some orthoptera, are the only animals of this 
division which have a visible ear. 
In the mouth of these animals there is a great analogy, 
which, according to the observations of M. Savigny, even 
extends, relatively at least to the hexapod insects, to those 
which can only suck fluid aliments. 
Those which are called grinders , because they have jaws 
proper for the trituration of food, always have them in lateral 
pairs, placed one before the other. The anterior pair are 
