MYCETOZOA 429 



of the sporangium becomes penetrated by an anastomosing network, 

 capillitium, of flat bands which are continuous with the outer cover- 

 ing (i). Soon after the differentiation of these protective and sup- 

 porting structures, the nuclei divide simultaneously by mitosis and 

 the cytoplasm breaks up into many small bodies. These uninucleate 

 bodies are the spores which measure 3-20/x in diameter and which 

 soon become covered by a more or less thick cellulose membrane (j), 

 variously colored in different species. 



The mature sporangium breaks open sooner or later and the 

 spores are carried, and scattered, by the wind. When a spore falls 

 in water, its membrane ruptures, and the protoplasmic contents 

 emerge as an amoebula (k, I). The amoebula possesses a single vesic- 

 ular nucleus and contractile vacuoles, and undergoes a typical amoe- 

 boid movement. It presently assumes an elongate form and one 

 flagellum or two unequally long flagella (Elliott, 1948) develop from 

 the nucleated end, thus forming a myxoflagellate (m, n) which under- 

 goes a peculiar dancing movement and is able to form short, pointed 

 pseudopodia from the posterior end. It feeds on bacteria, grows and 

 multiplies by binary fission (o-q). After a series of division, the myxo- 

 flagellate may encyst and becomes a microcyst (r). When the micro- 

 cyst germinates, the content develops into a myxamoeba (s) which, 

 through fusion with many others, produces the Plasmodium men- 

 tioned above. This is the life-cycle of a typical endosporous myceto- 

 zoan. 



In the genus Ceratiomyxa in which spores are formed on the sur- 

 face of sporophores, the development is briefly as follows: the 

 Plasmodium lives on or in decayed wood and presents a horn-like 

 appearance. The body is covered by a gelatinous hyaline substance, 

 within which the protoplasmic movements may be noted. The proto- 

 plasm soon leaves the interior and accumulates at the surf ace of the 

 mass; at first as a close-set reticulum and then into a mosaic of 

 polygonal cells, each containing a single nucleus. Each of these cells 

 moves outward at right angles to the surface, still enveloped by the 

 thin hyaline layer, which forms a stalk below. These cells are spores 

 which become ellipsoid and covered by a membrane when fully 

 formed. The spore is uninucleate at first, but soon becomes tetranu- 

 cleate. When a spore reaches the water, its content emerges as an 

 amoebula which divides three times, forming 8 small bodies, each 

 of which develops a flagellum and becomes a myxoflagellate. The 

 remaining part of the development is presumably similar to that of 

 the endosporous form. Morphology (de Bary, 1864, 1884; MacBride, 

 1922; Jahn, 1928; MacBride and Martin, 1934). 



