MESOPHYTE. 356 MESOZOIC EKA. intermediate soil moisture. The term is thus in contrast with hydrophj-te and xerophyte (qq.v. ). To tliis group belong the most common plants of the furc>>t and grass lands of equable climates. Cultivated areas with very few exceptions are mesophytic. Hydrophytes and xerophytes. then, may thus be regarded as extremes, the one adapt- ed to an extreme of moisture, the other of dry- ness. On account of the almost uniformly favor- able conditions, mesophytes are able to survive •without any striking adaptations such as are to be found among xeroph_-tcs and hydro|)hytes. However, with the exception of a few remarkably plastic hydrophytes, they exhibit maximum plas- ticity. It is perhaps not surprising that plas- ticity is found developed to a high degree among them, the sequence of periods of extreme mois- ture or extreme dryness tending to fix adapta- bility. The vegetation of mesophytic areas is nmch more dense than that in xerophytic or even in hydrophylic regions, and there is a far great- er wealth of species. The struggle for existence is thus more keen, and fewer representatives of the various species may be found, while a xer- ophytic or hydro|)hytic plant society may often be characterized by the dominance of one or two species. The keen competition which exists in mesophytic regions may perhaps account for the survival of forms with a high degree of plas- ticity. . other feature of mesophytic conditions is the richness of the soil, which doubtless ac- counts for the great diversity of plant forms, and for luxuriance which here reaches its climax in the plant world. The various mesophytic so- cieties are treated under the following heads: Forest; PRAiBrE: Me.^dow; and Pasture. MESOPOTA'MIA (Lat., from Gk. ^ao-o- raftla, sc. ;;, _</«'. country, country between the rivers, from fiico^, nicsos, middle + ■Trnrauo^, potamos, river). In the widest sense, all the country between the Tigris and Euphrates rivers from Armenia to the Persian Gulf: in a nar- rower and more eonnuon usage, the northern part of this territorv;, called to-day by the Arab name EhJezirah (the Island Peninsula), the southern portion (Babylonia) being known as Irak Arabi. In the Old Testament this territory is called Aram ynhnraijim (the Aram of the Two Rivers), of which the Greek name is prob- ably a translation: and Padrlnn Aram (the Plain of .Aram). The name, in the form ahrimn. is found in Egyptian inscriptions and in the Amar- na letters, though limited to the northwestern district between the Tigris and Belik. In the earliest times Mesopotamia seems to have been under native rulers, ami to have developed a civil- ization of its own which may have been the source of many features commonly attributed to the Assyrians, About B.C. 1.300 Rammannirari I. made it a part of Assyria. Aramiran-^ from the south invaded the land and settled there in the course of the Semitic migrations of the succeeding centuries. In B.C. .5.18 it passed under Persian rule, and later belonged successively to the Mace- donian. Syrian, an<I Parthian empires. The Ro- mans made it a province. In .303 .Tovian sur- rendered most of it to Persia, In the seventh century it came into the hands of the caliphs. After IO.tI.') much of the land was ruled by petty Seljukinn sultans. These were in turn con- <|uercd by the Mongols, who capture)! Bagdad in J2.iS and put the Caliph to death. The Osmanlis began their conquest early in the sixteenth cen- tury, and iu lliSS the land passed completely into their power. At present the jKjpulation is mainly Arali: most of the tribes are as inde- pendent of the Turkish Government as their brethren in Central Arabia, though the country is nominally divided between several Turkish vilayets. There are a few Kurds in the north, and a small mmiber of Armenian and Syrian Christians. The land is hilly in the north, but low and sandy to the south. After the Euphrates and Tigris, the chief rivers are the Khahur, Jaghjagha, and Belik. Bitumen is common, and a few petroleum wells are found. The most im- portant towns are L'rfa. Mardin. Xcsihin. Mosul, Ed-Dcir. and Rakka. In early times, when a good irrigation system was maintained, the land was fertile, populous, and the home of an advanced civilization. Owing to its situation, it was open to iniluences from both the east and the west, from Babylonia and Asia Elinor. Perhaps its most prosperous time was under Assyrian and Babylonian rule, but in the early Christian cen- turies it contained important cities, such as Edessa and Xisibis, and imder the caliphs the country also thrived. Today it is desert and uninhabited except along the banks of the nat- ural watercourses. Consult: Oppert. Expedi- tion scienti/ique en Mesopotamie (Paris, 1856-. 59) : Lady Anne Blunt, The Bedouin Tribes of the Euphrates (London, 1S80) : Sachau, Reise in Si/rien und Mesopotamia (Leipzig. 1883) ; Op- penheim, To»i ilittelmeer zum persisehen Golf (Berlin, 1809). See -Assyria; Babylo.via, MES'OZO'A (Xeo-Lat, nom. pi., from Gk. fiitrot. mrsofi. middle + ^^oy. :don. animal). A group of animals regarded as intermediate between the Protozoa and Metazoa. The name was proposed in ISTt! by E. van Beneden for a group of filifonn bodies living in the liquid bathing the "spongy bodies' or venous appendages (kidneys) of cephalopods. They resemble Infuso- ria, but are two-layered, and pass in their develop- ment through a gastrula stage. They were named Dicyenia by K'illiker. who. with others, consid- ered them as parasitic worms. Van Beneden re- garded these forms as constituting the type of n distinct branch or phylum of tlie animal king dom. These mesozoans are represented by two types of individtials. dilTcring externally: one ( 'nematogene' ) producing vermiform embryos, the other form Crhombogene') infusorifomi (but many-celled) .young. Packard suggested that Dicvema and allies ma.v l>e degenerate para- sitic plat.vlielminths derived originally from some low cestoid or treuiatode wojni. Parker and Haswell (1897) treat of them in an ap- pendix to the Civlenterata. and state that it has been proposed to call them the Planuloidea. from the re-*mlilan<-e which they bear to the planuin larva of the cadenterates. Sedg^vick ( Trxl-linok of Znolnfli/. 1808) is inclined to regard them as allied to the Trematoda. to the miracidium larva of which he asserts '"they do present some consid- erable resemblance." Consult Lankesler (edi- tor). .1 Treatise in Zoiilofiii. Part IV. (London and Xew York. 1903). MES OZOIC ERA. One of the main dins- ions of ;;i'. iliiyii' time, following the Paleozoic era anil preceding the Cenozoic era. It is subdi- vided into the Triassic. Jurassic, and Cretaceous periods. See Geolot.y.
