REPRODUCTION AND THE LIFE CYCLE 189 



be considered more appropriately in connection with the diseases due 

 to them. 



(a) Sporulation in Gregarinida. — A,s shown in the preceding chapter, 

 the number of gametes formed by the conjugating gregarines varies 

 within wide Umits. In ophryocystis, according to Leger ('07), there is 

 but one gamete formed in each cell, while only one sporoblast results 

 from the fusion of the gametes (see Fig. SO). In other gregarines there 

 are many gametes, which, as previously shown, may be sexually 

 differentiated. In most cases these gametes arise from the parent 

 gametocytes, which are enclosed together within one common cyst 

 wall (pseudoconjugation), but in the remarkable case of Schaudin- 

 nella henlece, described by Nusbaum ('03), the organisms are sexually 

 differentiated even before the gametocytes are formed, and pseudo- 

 conjugation of the gametocytes does not occur, each organism forming 

 its microgametes or macrogametes, as the case may be, independently 

 of one another, the gametes then meeting and fusing in the lumen of 

 the digestive tract. 



At the other extreme we may place the two species of diplocystis, 

 where the organisms pair immediately after entering the celom of 

 their hosts and continue to live in couples, while any individual 

 remaining solitary dies without further growth (Cuenot, 1901). 

 Here, therefore, pseudoconjugation appears to be a necessity for the 

 organisms. 



In all cases when the coupled gregarines are mature, the nucleus of 

 each divides by mitosis to form a residual nucleus and a so-called 

 " micronucleus" (Cufenot). The latter undergoes successive mitotic 

 divisions, and the resulting nuclei finally reach the periphery of the 

 cell, where the gametes are formed as buds. 



Development of the fertilized egg is essentially the same in all of 

 the gregarines. The fertilization nucleus (synkaryon) divides by a 

 primitive mitosis three successive times, and the sporoplasm separates 

 into eight parts, one around each of the nuclei. Eight sporozoites 

 are thus formed in the typical case, only one exception, that of seleni- 

 dium, where there are but four sporozoites, being known. 



The arrangement of the sporozoites in the sporocysts presents the 

 greatest variety, but has no importance from a systematic point of 

 view (Fig. 20). More important are the surrounding envelopes of the 

 bundle of sporozoites. In the majority of cases the sporocyst consists 

 of one (monocystis forms) or two tough, resistant membranes which 

 may become greatly hardened. When two are present, the inner or 

 endospore is smooth and relatively thin, forming a closely investing 

 sheath about the sporozoites. The second or outer covering, the 

 epispore, is more resistant and may consist of several layers (ophryo- 

 cystis), while it is frequently drawn out into spines, lateral processes, or 

 long filaments (Fig. 20, D, F). Under the proper conditions the 



