Excerpt from The Animal Kingdom, Vol. 13: Arranged in Conformity With Its Organization, by the Baron Cuvier, Member of the Institute of France, &C. &C. &C., With Supplementary Additions to Each Order
But the joints which compose the body have not always this sort of articulation: they are most usually united merely by ﬂexible membranes, or emboxed one Within the other; and then their motions are more varied, but do not possess the same force.
The system of organs on which the articulated animals are most similar to each other, is that of the nerves.
Their brain, situated on the oesophagus, and furnishing nerves to the parts which adhere to the head, is very small. Two cords, which embrace the oesophagus, are continued along the belly, uniting, from space to space, into double knots or ganglia, from which proceed the nerves of the body and Of the limbs. Each of these ganglia performs the functions of a brain, for the surrounding parts, and suffices to preserve their sensibility for a certain time, when the animal has been divided: If we add to this, that the jaws Of these animals, when they have any, are always lateral, and move from without to within, and not from top to bottom, and that there has not yet been discovered in any of them a distinct organ of smell, we shall have pretty nearly expressed all that may be said of them in general. But the existence of the organs of hearing; the existence, number, and form of those of sight; the product, and the mode Of generation *6 the nature of respiration; the existence of the organs of circulation; and even the colour of the blood, present great variations, which it will be necessary to study in the different sub-divisions.
A remarkable discovery on this subject is that of M. Herold, that in the egg of the crustacea and arachnida, the vitellus communicates with the interior by the back. See his dissertation on the egg of spiders, Marburg, 1824, and that of M. Rathke on the egg of the Astaci, Leipzig, 1829.
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