His “first system” was applied to numerous places in Holland, notably Nijmwegen, Breda and Bergen-op-Zoom. Mannheim in Germany was also fortified in this way, while the “secondsystem” was applied to Belgrade and Temesvár in eastern Europe.
His son, Gosewijn Theodor van Coehoorn, wrote his life (re-edited Syperstein, Leeuwarden, 1860). See also v. Zastrow, Geschichte der beständigen Befestigung (Leipzig, 1828); von Brese-Winiari, Über Entstehen und Wesen der neueren Befestigungsmethode (1844); Cosseran de Villenoisy, Essai historique sur la fortification (1869); Mandar, Architecture des forteresses (1801); Krayenhoff, Verhandeling over de erste versterkingsmanier van Coehoorn (Hague, 1823); Bosscha, Nederlandsche heldend te Land (Amsterdam, 1838); Dewez, Histoire de Belgique (Brussels, 1823); Ypey, Narratio de rebus gestis Mennonis Cohorni (1771); Hennert, Dissertation sur la fortification permanente (1795); Böhms, Gründliche Anleitung zur Kriegsbaukunst (1776); Axiomatas of allgemeene bekentnisse over de Vestinghbouw door Menno Baron van Coehoorn, Uytgewerkt door E. W. Berg (MS. in Dutch Ministry of War); Bousmard, Essai général de fortification (1797); also the article [Fortification and Siegecraft].
COELENTERA, a group or grade of the animal kingdom, the zoological importance of which has risen considerably since the time (1887) of the publication of the first article under that heading in the Ency. Brit. (9th edit.), even though their numbers have been reduced by the elevation of the Sponges or Porifera to the rank of an independent Phylum under the title Parazoa (W. J. Sollas, 1884). For the Coelentera thus restricted, the term Enterocoela, in contrast to Coelomocoela (the old Coelomata), was suggested by E. R. Lankester (1900).
From the more complex colonial Protozoa the Coelentera are readily separated by their possession of two distinct sets of cells, with diverse functions, arranged in two definite layers,—a condition found in no Protozoan. The old criterion by which they and other Metazoa were once distinguished from Protozoa, namely, the differentiation of large and small sexual cells from each other and from the remaining cells of the body, has been broken down by the discovery of numerous cases of such differentiation among Protozoa. The Coelentera, as contrasted with other Metazoa (but not Parazoa), consist of two layers of cells only, an outer layer or ectoderm, an inner layer or endoderm. They have hence been described as Diploblastica. In the remaining Metazoa certain cells are budded off at an early stage of development from one or both of the two original layers, to form later a third layer, the mesoderm, which lies between the ectoderm and endoderm; such forms have therefore received the name Triploblastica. At the same time it is necessary to observe that it is by no means certain that the mesoderm found in various groups of Metazoa is a similar or homologous formation in all cases. A second essential difference between Coelentera and other Metazoa (except Parazoa) is that in the former all spaces in the interior of the body are referable to a single cavity of endodermal origin, the “gastro-vascular cavity,” often termed the coelenteron: the spaces are always originally continuous with one another, and are in almost every case permanently so. This single cavity and its lining serve apparently for all those functions (digestion, excretion, circulation and often reproduction) which in more complex organisms are distributed among various cavities of independent and often very diverse origin.
In the Coelentera the ectoderm and endoderm are set apart from one another at a very early period in the life-history; generally either by delamination or invagination, processes described in the article Embryology. Between these two cell-layers a mesogloea (G. C. Bourne, 1887) is always intercalated as a secretion by one or both of them; this is a gelatinoid, primitively structureless lamella, which in the first instance serves merely as a basal support for the cells. In many cases, as, for example, in the Medusae or jelly-fish, the mesogloea may be so thick as to constitute the chief part of the body in bulk and weight. The ectoderm rarely consists of more than one layer of cells: these are divisible by structure and function into nervous, muscular and secretory cells, supported by interstitial cells. The endoderm is generally also an epithelium one cell in thickness, the cells being digestive, secretory and sometimes muscular. Reproductive sexual cells may be found in either of these two layers, according to the class and sub-class in question. The mesogloea is in itself an inert non-cellular secretion, but the immigration of muscular and other cells into its substance, from both ectoderm and endoderm, gives it in many cases a strong resemblance to the mesoderm of Triploblastica,—a resemblance which, while probably superficial, may yet serve to indicate the path of evolution of the mesoderm.
The Coelentera may thus be briefly defined as Metazoa which exhibit two embryonic cell-layers only,—the ectoderm and endoderm,—their body-cavities being referable to a single cavity or coelenteron in the endoderm. Their position in the animal kingdom and their main subdivisions may be expressed in the following table:—
In the above-given classification, the Scyphomedusae, formerly included with the Hydromedusae as Hydrozoa, are placed nearer the Anthozoa. The reasons for this may be stated briefly.