CHAPTER XVI 

 THE SPOROZOA : III. THE NEOSPORIDIA 



A TYPICAL member of the subclass Neosporidia is a parasite of 

 which the life-cycle is initiated by the liberation from the spore 

 of one or more amcebulse within the body of the host, in the digestive 

 tract in all known cases. For this initial amcebula-phase Stempell's 

 term, planont (i.e., " wanderer "), may be employed conveniently, 

 since in no case does it remain in the lumen of the digestive tract, 

 but penetrates into the wall of the gut, and in most cases migrates 

 thence into some organ or tissue of the host, where it lives and 

 multiplies actively, being usually at this stage an intracellular 

 parasite, in some cases, however, occurring free in the blood or 

 lymph. 



The planont-phase is succeeded typically by a plasmodial phase, 

 which arises in some cases by simple growth of the amcebula 

 (probably then a zygote), accompanied by multiplication of its 

 nuclei ; in other cases by association together and cytoplasmic 

 fusion of at least two distinct amcebulse, of which the nuclei remain 

 separate. The plasmodial stage is very characteristic of this sub- 

 class ; it represents the principal or " adult " trophic phase of the 

 parasite, and is also the spore-forming phase ; and, as the name 

 Neosporidia implies, the production of spores begins, as a rule, 

 when the plasmodium is still young, and continues during its 

 growth. 



In some cases, however, no plasmodium is formed, but the 

 planont-phase is succeeded by uninucleate " meronts " or schizonts, 

 which multiply by fission and give rise ultimately to sporonts in 

 which spore-formation sets a limit to the growth. In such forms 

 the general course of the life-cycle is not essentially different in 

 any way from that of a member of the Telosporidia, such as Coc- 

 cidium. The tendency, therefore, of many Neosporidia to form 

 spores during the trophic phase cannot be used to frame a rigorously- 

 exact definition of the group. A more distinctive characteristic 

 of the subclass is the complete absence of flagellated phases in 

 any part of the life-cycle, and more especially the fact that 



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