Their nervous system consists of a ring, which surrounds the gullet, and is placed at a short distance from the mouth. In this ring the nervous trunks have their origin. In relation to the senses, that of touch is highly developed. Certain branching tentacula, which surround the mouth, fashioned like nippers, and the ambulacral tentacles, are its principal organs. They appear to be altogether destitute of organs of sight. It has sometimes been argued that four or five red points at the summit of the dorsal face are eyes; but this opinion has not been maintained, nor has any crystalline lens been found in these spots to justify it. Captain de Condé states that he examined a sea-urchin with long spears in a pool of water, which he tried to catch, when he saw it direct its flight towards his hand, all its defences being erect. Surprised at this manœuvre, he tried to seize it from another quarter; its spines were instantly directed to the other side. "I have thought from that time that the urchin saw me, and prepared to resist my attack. In order, however, to satisfy myself whether or not the movement in the water caused by my approach might have produced the effect described, I repeated the experiment with greater caution. But the creature always directed its spines in the direction of the object which threatened it, whether it was in the water or out of it." He satisfied himself that these animals certainly could see, and that their spines served them as a means of defence.
These wonderful spines, this calcareous envelope, this armour so marvellously studded, with which nature has so bountifully provided the Echinidæ, appear to have been insufficient, inasmuch as these very spines, in order to secure the safety of the animal, are gifted with the power of hollowing a dwelling for themselves out of solid rocks of the hardest material, such as granite and sandstone. They fix themselves to its surface by means of their tentacles; they make an incision by means of their strong teeth, removing the débris with their spines as fast as it is produced. When the hole is large enough, they entrench themselves in it, with their spines and their threatening pikes levelled to protect them from all external assaults. To M. Caillaud, the conservator of the museum of Nantes, we are indebted for an excellent account of the manner in which this buccal apparatus is made to operate. "The Lantern of Aristotle," says this author, "forms the mandibullary apparatus; the teeth are five in number, and they may as well receive the denomination of a series of saws and picks as of teeth, for they are surprisingly adapted to the excavation of holes in the hardest rock. These five picks are about the eighth of an inch long, and they serve the sea-urchin at once as masticators and excavating implements. In opening the jaws, these five teeth strike the stone forcibly rather than scrape it." This property of hollowing their dwelling out of the solid rock appears, however, to belong to only a small number of the Echinidæ; most of them are content to hide themselves under the stones, while the species having the spines slender and the shell very thin bury themselves in the sand, with which they cover themselves entirely, leaving only a small hole to breathe through. The Spatangus, which is furnished with short thick spines on the under part of its body, which spread out at the extremity like the channel of a spoon, proceeds with its mining operations as follows, according to Mr. Jonathan Franklin. "Figure to yourself, reader, the animal on the sea-shore. He commences his operations by turning the lower spines in such a manner as to form a hollow on the sand bank, in which he sinks by his own weight; but as he sinks, a great number of the spines are brought into action, throwing up the sand with increased activity, while the sand thrown up, returning again, soon covers the body of the worker, and he has soon buried himself beneath the surface. In this situation the long hair-like spines situated upon the back begin to play their part; they prevent the sand from entirely covering the animal by forming a little round hole, through which water is introduced to the mouth and respiratory organs." The hiding-place of the sea-urchin is, however, easily detected in the sand by the hole thus arranged for the respiration of the animal, and the fishermen think they can predict storms according to the depth of the hole.
The Echinidæ are reproduced by eggs, which are red and nearly microscopic. As it issues from the egg the larva has the appearance of a very minute fish. It is not at once converted into the perfect animal, but undergoes a certain metamorphosis analogous to that of the caterpillar into the butterfly. But, as we have already stated in treating of the Asteriæ, it produces, at a certain stage, by some sort of internal process of generation, a sea-urchin, which, being at first only an organ of the larva, begins to live an independent life when the nursing larva has destroyed itself. The manner in which the urchin unfolds itself at the expense of the larva is quite analogous to that which the asterias present: it is another case of alternate generation, of which our space does not permit us to give even a general outline.
Sea-urchins are found in every sea; they dwell in sandy bottoms, and sometimes upon rocky ground. They are caught with wooden pincers when in shallow water; when found at the water's edge, they may be taken by a gloved hand.
The urchin, like the crab, which it also resembles in taste, becomes red when boiled; only certain species are comestible, however. In Corsica and Algeria the Melon-shaped Urchin (Echinus melo) is much esteemed. In Naples and in the French ports of the Channel the Echinus lividus is eaten. In Provence the Common Sea-urchin (Echinus esculentus and Echinus granulosus) are the favourites.
Sea-urchins are eaten raw like oysters. They are cut in four parts, and the flesh taken out with a spoon; they are sometimes, but more rarely, dressed by boiling, and eaten from the shell like an egg, using long sippets of bread: hence the name of sea-eggs, which they bear in many countries.
Plate IX.—Sea Urchins lodged in the rocks they have excavated.
Sea-eggs were a choice dish upon the tables of the Greeks and Romans; they were then served up with vinegar or hydromel, with the addition of mint or parsley. When Lentulus feasted the priest of Mars—the Flamen Martialis—this formed the first dish at supper. Sea-eggs also appeared at the marriage feast of the goddess Hebe. "Afterwards," says the poet, "came crabs and sea-urchins, which do not swim in the sea, but content themselves by travelling on the sandy shore." For my own part, I have only once partaken of sea-urchin, and it appeared to me to be food fit for the gods; but perhaps the circumstances sufficiently explain this dash of culinary enthusiasm. The Reserve Restaurant at Marseilles has not always been the vast stone edifice we now behold, backed majestically by the mountain, and fronting the sea on the promenade of the Corniche du Prado. In 1845 it rose quite at the entrance of the port, a small glass cage, suspended as it were by a magic thread between the heavens and the sea. From this aërial dwelling, overhanging with unheard-of audacity the waters which surrounded it on all sides, we gazed on the most wonderful prospect in the world, and reposed ourselves while enjoying this intoxicating scene, during which the ships were continually entering the port, passing under our very feet. It was in this enchanted palace that sea-urchins were served up, supported by the traditional bouillabaise.