THE SPOROZOA 



283 



no more than two being formed in some genera, hence termed 

 disporous, but more usually they are produced in great numbers, 

 and all stages of the development of the spores are commonly to be 

 found present at the same time in a given individual. Since, 

 therefore, sporulation does not, as in Telosporidia, indicate a 

 cessation of growth and nutritive activity on the part of the 

 parasite, it is not accompanied by encystment of the sporont. 

 Occasionally, however, the ectoplasm may secrete a gelatinous 

 envelope, when reproduction commences (e.g. Myxidium giganteum, 

 Doflein). 



In some cases, e.g. Myxidium lieberkiihnii, Biitschli, spore-forma- 



vac_ 



Stages in spore-formation. All the figures are from Myxobolus ellipsoidts, Thel. (par. Tiiica), 

 except a and /, which are from M. pfeifferi, Thel. (par. liarbus). a, differentiation of the pan- 

 sporoblast (psp). b, pansporoblast with two nuclei, c and d, pansporoblasts with six and ten 

 nuclei respectively ; in d, four of the nuclei are degenerating, e, pausporoblast segmented into 

 two definitive sporoblasts, each with three nuclei. In the next four figures the definitive 

 sporoblast, or the spore produced from it, is alone figured. /, definitive sporoblast segmented 

 into three masses, the capsulogenous cells (c.g.c) and the sporoplasm (sp.p), within an envelope, 

 the spore membrane (sp.7). g, more advanced stage, k, spore completely developed, with two 

 polar capsules and sporoplasm containing an iodinophilous vacuole. i, abnormal spore con- 

 taining six polar capsules. ;;>, pausporoblast; n, nuclei; sp.bl, definitive sporoblast; r.n, 

 residuary nuclei ; c.g.c, capsulogenous cells ; sp.p, sporoplasm ; sp.m, spore membrane ; vac, 

 vacuole ; r.p.c, rudiment of p.c, polar capsule ; n.p.c, nuclei of polar capsules ; iod.vac, iodino- 

 philous vacuole ; n.sp., nuclei of sporoplasm. (After Thelohan.) 



tion has been observed to vary with the seasons, being in abeyance 

 in the winter, but proceeding actively in the warmer months. 



The first sign of spore - formation is the concentration of 

 protoplasm round one of the nuclei of the endoplasm, to form a 

 little spherical corpuscle, the pansporoblast of Gurley ("primitive 

 sphere " of Thelohan). Not all the nuclei of the endoplasm, 

 however, are used up for the formation of pansporoblasts ; a 

 certain number may be left over as residuary nuclei, at least in 

 the Disporea (Fig. 91). The pansporoblast is separated from the 

 surrounding endoplasm by a thin pellicle or envelope of tougher 

 protoplasm. In preparations a space may appear round it (Fig. 

 90, a), which is the result of shrinkage caused by preserving 

 reagents, and is not present in the living condition. The nucleus 



