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602 JE MM APES JENA more than half an inch high, produce some of the largest jelly fishes ; as the one which by subdivision into saucer-like contractions forms the ephyra, with a marginal fringe of tentacles. In our common white sun fish, the four cres- centic rosy figures, forming a cross by their union in the centre, are accumulations of eggs. Some of the jelly fishes in our waters formed from these self-dividing hydroids are as large as the largest wash tub, with tentacles extend- ing 20 or 30 ft. ; these are of a deep claret color, and possess in a remarkable degree the sting- ing or nettling property which has given the scientific name to the class. In the Portuguese man-of-war, some of the community move the whole establishment, some secure prey with their lasso cells and eat and digest for the family, and some produce the buds from which the young jelly fishes arise ; and none of these take up or interfere with the work of the others. In the same way the hydroid cam- panularia produces the jelly fish tiaropsig, with its edge beautifully fringed. Some very handsome jelly fishes do not originate from any hydroid, but reproduce themselves in the usual way by eggs. For the greater part of the year the eggs remain torpid, then a polyp-like vegetation arises, with buds which flower-like become rapidly developed into more highly or- ganized free jelly fishes; these animal flowers, as they have been called, are so sensitive that they are instantly killed by a change from salt to fresh water. They are very voracious, feed- ing upon minute fishes, crustaceans, almost any small marine creatures, decaying animal or vegetable matters, and even their own species ; they move with the rapidity and elegance of birds of prey, securing their victims with pre- cision by means of their nettle-armed tentacles, and performing these acts in a manner which would hardly be expected in a transparent mass of jelly. A nervous system is present ; and the form is in many capable of remarkable changes. For details on their structure, see Forbes's work on the British naked-eyed me- dusae ; two papers by Prof. Agassiz in the " Memoirs of the American Academy of Arts and Sciences," vol. iv., part 2, 1850 ; and vol. iii. of Agassiz's " Contributions to the Natural History of the United States" (4to, Boston, 1860). The well known phosphorescence of the ocean is largely due to the light emitted by jelly fishes, shining like globes of fire, spark- ling like stars, or diffusing a pale luminousness ; this is most remarkable when the water is agi- tated by a vessel's keel, and on the coast line or amid breakers, where these creatures often serve to mark the course of the mariner. The number of these jelly fishes, often very minute, is beyond calculation or expression, especially in northern waters, where they form the food both of the small crustaceans and other animals upon which the right whales feed, which also devour the jelly fishes in immense numbers. JEMMAPES, or Gemappe, a village of Belgium, in the province of Hainaut, on the river Haine and on the canal from Mons to Conde, 3 m. W. of Mons; pop. in 186T, 11,405. The place contains several breweries, tanneries, forges, flour mills, a salt refinery, and extensive soap works. It is noted for a battle, Nov. 6, 1792, between the French under Dumouriez and the Austrians under Duke Albert of Teschen. The republican forces numbered about 40,000; the Austrian army was equally strong, but it was so posted that only its centre, consisting of 18,000 men, could be brought into action. These troops were intrenched, however, be- tween Jemmapes and Mons, and their position was defended by 14 redoubts, mounting nearly 100 pieces of artillery. The battle begun at j daybreak with an attack by a French column under Beurnonville, who turned the Austrian flank and carried the redoubts on the left. A simultaneous attack on the centre was also suc- cessful, and the victory was complete. The Austrian loss was about 5,000, the French 6,000 ; but the consequences of the battle, the first regular engagement won by the republican forces, were very important to both parties. Most of the cities of the Netherlands surren- dered to the victors without opposition; and when Belgium was annexed to the French re- public Jemmapes gave its name to a depart- ment comprising nearly the whole of Hainaut. JENA, a town of Germany, in the grand duchy of Saxe-Weimar-Eisenach, on the Saale, 12m. S. E. of Weimar; pop. in 1871, 8,197. It is partly surrounded by steep barren moun- tains, and consists of the town proper, through which flows the little river Leutra, and several suburbs. It is the seat of a supreme court of appeals for the grand duchy, and for several neighboring duchies, and the principalities of Reuss, and contains a ducal palace, three Luther- an churches, a Roman Catholic church, three hospitals, a lunatic asylum, &c. The country around Jena is so beautiful that Charles V. is said to have placed it in that respect next to Florence. The foundation of its celebrated university was laid by the elector John Frede- rick the Magnanimous in 1547, when as a pris- oner of Charles V. he was removed to Jena, where he was to meet his three sons. The university of Wittenberg having been wrested from him, his object was to establish in its stead a seat of learning at Jena which should become a nursery of science and of the doc- trines of the reformation. The institution was sanctioned by the emperor Ferdinand I. in 1557, and inaugurated Feb. 2, 1558; and its 300th anniversary was celebrated Aug. 15-17, 1858. In connection with it are a philological and a theological seminary, a clinique, an anatomical theatre, an obstetric and pharmaceutical estab- lishment, an institution for natural and mathe- matical sciences, one for agricultural science, and another founded in 1849 for political sci- ence, a botanical garden, an observatory, a mu- seum of mineralogy, natural curiosities, archro- ology, and oriental coins, and a library with more than 200,000 volumes. Jena holds a