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 commonly called the Treasury of Atreus, is just outside the Lion Gate. It consists of a circular domed chamber, nearly 50 ft. in diameter and in height; a smaller square chamber opens out of it. It is approached by a horizontal avenue 20 ft. wide and 115 ft. long, with side walls of squared stone sloping up to a height of 45 ft. The doorway was flanked with columns of alabaster, with rich spiral ornament, now in the British Museum; and the rest of the façade was very richly decorated, as may be seen from Chipiez’s fine restoration. The inside of the vault was ornamented with attached bronze ornaments, but not, as is sometimes stated, entirely lined with bronze. It is generally supposed that these tombs, as well as those excavated in the rock, belong to a later date than the shaft-tombs on the Acropolis.

 MYCETOZOA (Myxomycetes, Schleimpilze), in zoology, a group of organisms reproducing themselves by spores. These are produced in or on sporangia which are formed in the air and the spores are distributed by the currents of air. They thus differ from other spore-bearing members of the animal kingdom (which produce their spores while immersed in water or, in the case of parasites, within the fluids of their hosts), and resemble the Fungi and many of the lower green plants. In relation with this condition of their fructification the structures formed at the spore-bearing stage to contain or support the spores present a remarkable resemblance to the sporangia of certain groups of Fungi, from which, however, the Mycetozoa are essentially different.

Although the sporangial and some other phases have long been known, and Fries had enumerated 192 species in 1829, the main features of their life-history were first worked out in 1859–1860 by de Bary (1 and 2). He showed that in the Mycetozoa the spore hatches out as a mass of naked protoplasm which almost immediately assumes a free-swimming flagellate form (zoospore), that after multiplying by division this passes into an amoeboid phase, and that from such amoebae the plasmodia arise, though the mode of their origin was not ascertained by him.

The plasmodium of the Mycetozoa is a mass of simple protoplasm, without a differentiated envelope and endowed with the power of active locomotion. It penetrates the interstices of decaying vegetable matter, or, in the case of the species Badhamia utricularis, spreads as a film on the surface of living fungi; it may grow almost indefinitely in size, attaining under favourable conditions several feet in extent. It constitutes the dominant phase of the life-history. From the plasmodium the sporangia take their origin. It was Cienkowski who (in 1863) contributed the important fact that the plasmodia arise by the fusion with one another of numbers of individuals in the amoeboid phase—a mode of origin which is now generally recognized as an essential feature in the conception of a plasmodium, whether as occurring among the Mycetozoa or in other groups (7). De Bary clearly expressed the view that the life-history of the Mycetozoa shows them to belong not to the vegetable but to the animal kingdom.

The individual sporangia of the Mycetozoa are, for the most part, minute structures, rarely attaining the size of a mustard-seed, though, in the composite form of aethalia, they may form cake-like masses an inch or more across (fig. 21). They are found, stalked or sessile, in small clusters or distributed by the thousand over a wide area many feet in diameter, on the bark of decaying trees, on dead leaves or sticks, in woods and shrubberies, among the stems of plants on wet moors, and, generally, at the surface in localities where there is a substratum of decaying vegetable matter sufficiently moist to allow the plasmodium to live. Tan-heaps have long been known as a favourite habitat of Fuligo septica, the plasmodia of which, emerging in bright yellow masses at the surface prior to the sporangial (in this case aethalial) phase, are known as “flowers of tan.” The

film-like, expanded condition of the plasmodium, varying in colour in different species and traversed by a network of vein-like channels (fig. 5), has long been known. The plasmodial stage was at one time regarded as representing a distinct group of fungi, to which the generic name Mesenterica was applied. The species of Mycetozoa are widely distributed over the world in temperate and tropical latitudes where there is sufficient moisture for them to grow, and they must be regarded as not inconsiderable agents in the disintegrating processes of nature, by which complex organic substances are decomposed into simpler and more stable chemical groups.

Classification.—The Mycetozoa, as here understood, fall into three main divisions. The Endosporeae, in which the spores are contained within sporangia, form together with the Exosporeae, which bear their spores on the surface of sporophores, a natural group characterized by forming true plasmodia. They constitute the Euplasmodida. Standing apart from them is the small group of the mould-like Sorophora, in which the amoeboid individuals only come together immediately prior to spore-formation and do not completely fuse with one another.

A number of other organisms living on vegetable and animal bodies, alive or dead, and leading an entirely aquatic life, are included by Zopf (31) under the Mycetozoa, as the “Monadina,” in distinction from the “Eumycetozoa,” consisting of the three groups above mentioned. The alliance of some of these (e.g. Protomonas) with the Mycetozoa is probable, and was accepted by de Bary, but the relations of other Monadina are obscure, and appear to be at least as close with the Heliozoa (with which many have in fact been classed). The limits here adopted, following de Bary, include a group of organisms which, as shown by their life-history, belong to the animal stock, and yet alone among animals they have acquired the habit, widely found in the Vegetable kingdom, of developing and distributing their spores in air.

