314 Sporozoa 



tiated from the rest of the protoplasm. Each such "cell" is the initial 

 stage of a sporoblast, or of a disporous pansporoblast if it is to produce 

 two spores. In at least some species, the differentiation of a sporoblastic 

 and a somatic nucleus is already apparent in the young binucleate tropho- 

 zoite (Fig. 6. 27, B). Division of the sporoblastic nucleus during the 

 growth phase results in a sporoblast with 6-8 nuclei, or a pansporoblast 

 with a larger number of nuclei (Fig. 6. 27, C-E), the number varying 

 with the number of polar capsules to be produced. If a pansporoblast is 

 developed, it later divides into two sporoblasts. 



Six nuclei appear in each developing spore of Leptotheca ohlmacheri 

 (70; Fig. 6. 27, D, E), Two acquire differentiated zones of cytoplasm and 

 become the cystogenous cells which gradually enclose the rest of the 

 young spore and produce the valves of the spore membrane. Two other 

 nuclei and their surrounding masses of cytoplasm become the capsulog- 

 enous cells which produce the polar capsules. The remaining two nuclei 

 become the haploid nuclei of the sporoplasm. As a rule, however, young 

 spores of species with two polar capsules contain eight nuclei (99). Two 

 of these, the so-called residual nuclei, degenerate during later develop- 

 ment. The development of the other six follows the course outlined for 

 Leptotheca. 



The spore membrane is composed of two valves united in a suture 

 which may be either straight (Fig. 6. 26, B) or irregular (Fig. 6. 28, O), 

 and is often marked by a sutural ridge formed by the thickened edges of 

 the valves. The valves may be smooth or may be decorated with striations, 

 ridges, or papillae. The spores of some species are ovoid, those of others 

 may be spindle-shaped or somewhat asymmetrical, and the valves are 

 sometimes drawn out into horns or spines (Fig. 6. 28). Each polar capsule 

 lies near a pore which opens through the spore membrane in or near 

 the sutural plane; or sometimes two adjacent capsules share a common 

 pore. The mature spore usually contains a single sporoplasm, although 

 two may be present as in Leptlwtheca oJilmacheri (70). The single sporo- 

 plasm usually contains two nuclei, and in either case the sporoplasmic 

 nuclei are haploid (74, 97, 99). A fairly large inclusion ("iodinophilous 

 vacuole"), which is stained reddish-brown with iodine, is characteristic 

 of the sporoplasm in certain genera (Family Myxobolidae), but not in 

 the majority. The number of spores produced by each trophozoite varies 

 in different cases, and a given species may be typically monosporous, dis- 

 porous, or polysporous. However, this is not a rigidly fixed characteristic 

 and all three types of sporulation are sometimes observed within a single 

 species. 



Although the occurrence of meiosis is well established, the stage at 

 which this process apparently occurs varies in the descriptions of different 

 species. In some cases (97, 98), meiosis occurs in one of the last nuclear 

 divisions in development of the sporoblast, the products being the hap- 



