298 PROTOZOOLOGY 



course of sporangium-formation, foreign bodies are thrown out 

 of the body, and around each sporangium there is secreted a 

 wall which, when mature, possesses a wrinkled appearance (h). 

 The wall continued down to the substratum as a slender stalk of 

 varying length, and in many genera the end of a stalk spreads into 

 a network over the substratum, which forms the base, hypothal- 

 lus, for the stalk. With these changes the interior of the spo- 

 rangium becomes penetrated by an anastomosing network, 

 capillitium, of flat bands which are continuous with the outer 

 covering (i). Soon after the differentiation of these protective and 

 supporting structures, the nuclei divide simultaneously by 

 mitosis and the cytoplasm breaks up into as many small bodies 

 as are nuclei. These uninucleate bodies are the spores which 

 measure 3-20yu in diameter and which soon become covered by a 

 more or less thick cellulose membrane (j), variously colored in 

 dilTerent 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 con- 

 tents emerge as an amoebula (k, I). The amoebula possesses a 

 single vesicular nucleus and contractile vacuoles, and undergoes 

 a typical amoeboid movement. It presently assumes an elongate 

 form and protrudes a flagellum from the nucleated end, thus 

 developing into a myxoflagellate (zoospore or swarmer) (m, n) 

 which undergoes 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-g). 

 After a series of division, the myxoflagellate may encyst and be- 

 comes a microcyst (r). When the microcyst germinates, the con- 

 tent develops into a myxamoeba (s) which, through fusion with 

 many others, produces the Plasmodium mentioned before. This 

 is the life-cycle of a typical endosporous mycetozoan. 



In the genus Ceratiomyxa in which spores are formed on the 

 surface 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 sub- 

 stance, within which the protoplasmic movements may be noted. 

 The protoplasm soon leaves the interior and accumulates at the 

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

 a mosaic of polygonal cells, each containing a single nucleus. 



