MYXOSPORIDIA 



183 



is not simple (fig. 97), and the spore itself is surrounded by a bivalved shell or sporo- 

 cyst and contains polar capsules in addition to the amoeboid germ (fig. 97, G, H). The 

 valves of the sporocyst and the polar capsules are really differentiated nucleate cells, 

 so that each spore is an aggregate of cells rather than one cell, though only a single 

 amcebula issues from a spore. The accounts of spore formation vary somewhat 

 according to the different workers. 



Spore formation is usually very complicated and there are differences of opinion 

 as to the interpretation of various stages, particularly as to whether conjugation 

 occurs therein. The process is initiated by the concentration of cytoplasm around 

 one of the nuclei of the endoplasm, so that a small spherical mass or initial corpuscle 

 is produced, the pansporoblast (Gurley) or primitive sphere (Thelohan). Some 

 authors state that a pansporoblast really results from a conjugation of two ini'ial 

 corpuscles (fig. 97, A D). Nuclear multiplication occurs within the pansporoblast 



H 



FIG. 97. Myxobolns pfeffiri. Spore formation. A, reproductive cell from plasmodial 

 trophoz<>ite ; B, cell divided unequally into two ; C, smaller cell forming envelope to larger 

 one ; D, pinspornblast formed by union of two forms like C ; E, multinucleate pansporoblas% 

 two of the nuclei being those of the envelope ; F, pinsporob'ast divided into two multinucleate 

 sporoblasts ; G, spore differentiation ; />, two parietal cells forming sporocyst ; be, polar cap- 

 sules ; am, binucleate amoebula ; H, ripe spore in which the two nuclei of the amcebula have 

 fused. (After Keysselitz.) 



(fig- 97> E )i and sooner or later two multinucleate sporoblasts are formed within it 

 (fig. 97, F). Each sporoblast gives rise to a single spore, which consists of a sporo- 

 cyst or envelope composed of two valves each secreted by a cell, two polar capsules 

 each secreted by a cell, and the sporoplasm or amcebula which becomes binucleate 

 (fig. 97, G). During the process of spore formation (fig. 97) various vegetative and 

 reduction nuclei maybe produced, in addition to those which are essentially involved 

 in spore formation, and the sporocyst cells may be developed early. 



Each spore contains two (figs. 94, 95) or more polar capsules which are clearly 

 visible in the fresh condition. Each polar capsule is a hollow, more or less pear- 

 shaped body, secreted by a cell and having a well defined contour. Within it, a 

 long, delicate, elastic filament, the polar filament, is formed, and lies spirally coiled 

 in the polar capsule until just before the emergence of the amcebula from the spore 

 (fig- 95)- The polar filament is ejected, probably under the influence of the digestive 



