MYCETOZOA. 909 



Union of the Myxamoebae in a fusion-plasmodium is characteristic of 

 the two other sub-groups of Mycetozoa, the Exo- and Endo-sporea. Two 

 or three unite first of all ; the large Myxamoeba thus formed serves as 

 a focus of attraction, and by the repeated addition and fusion of other 

 Myxamoebae, it eventually becomes a fusion-plasmodium, or simply a 

 plasmodium. The plasmodia vary in size ; the majority are either just 

 visible or just invisible to the naked eye ; those of the Physareae, 

 however, cover surfaces of lin. to ift. They have as a rule the shape 

 of a branched tree or network of moving protoplasm. Lycogala epidendron 

 is an exception ; it has the shape of cylindrical, varicose, slightly branched 

 threads. Movement takes place by the extension of protoplasmic processes 

 in one direction and their withdrawal in other quarters. If they should 

 happen to be extended simultaneously and energetically in different 

 directions, the result is a rending of the plasmodium into a number of 

 separate portions. These portions, like the portions formed by artificial 

 section of a plasmodium, behave in all ways as so many plasmodia. 

 From a structural point of view, a plasmodium consists of a clear, dense 

 superficial protoplasm, with a granular fluid central portion or medulla. 

 The granules are of various kinds ; some of them in the Calcariaceae^ 

 e. g. Fuligo, or the * flowers of tan/ consist of Calcium carbonate. Yellow, 

 red, violet, or brown pigment is met with in some instances. Vacuoles 

 are present, and are sometimes contractile. The nuclei of the Myx- 

 amoebae persist. The surface is clothed by a soft, sticky, pellucid coat 

 or hypothallus, to which earth and some other foreign bodies adhere, 

 and which may be left behind as a trail in the onward movement of the 

 plasmodium. If the conditions of life become unfavourable before maturity 

 is attained, the plasmodium passes into a resting-phase known as the 

 macrocyst, or thick-walled cyst. It breaks up into portions of unequal 

 size, which become globular and develope in succession two membranes. 

 The encysted protoplasm is only set free after a prolonged soaking of 

 the macrocysts. But if the plasmodium is ripe for sporulation, its 

 resting-phase, the sclerotium, has a different character. All processes are 

 withdrawn by degrees, whilst foreign bodies are extruded and the granules 

 of the protoplasm evenly distributed. The mass becomes rounded, and is 

 resolved into minute globular or polyhedral cells ; it becomes in consistence 

 wax-like and finally brittle. Its cells have one or more vacuoles, and in 

 two instances a cellulose membrane. They are bound together by an 

 outer homogeneous layer covering the mass. If placed in water the scler- 

 otium swells ; its cells acquire one or more contractile vacuoles ; their 

 membrane, if present, is dissolved ; the liberated portions of protoplasm 

 become amoeboid and fuse to reconstitute the plasmodium. 



As soon as a plasmodium has attained its definitive growth, it comes 

 to the surface of the decaying wood, &c., whatever it inhabits, and proceeds 



