74 THE ANIMAL PARASITES OF MAN 



The SIZE OF THE COCCIDIIDA, corresponding as a rule to the habi- 

 tat, is usually small, but there are species that attain a diameter of 

 i mm. Their FORM is globular, oval, or elliptical. External appen- 

 dages are lacking, at least during the vegetative period of their 

 life, which is spent in epithelial cells, within which they increase 

 in size ; as a rule only one is present in each cell, rarely more. 

 The BODY SUBSTANCE is composed of a more or less finely granu- 

 lated or distinctly alveolar protoplasm which exhibits no differen- 

 tiation in ecto- and endo-sarc. All species possess a nucleus that 

 enlarges with their growth ; sometimes it only shows through the 

 plasma as a lighter spot, or may even be quite concealed. It is 

 vesicular in shape, and besides containing very delicate threads of 

 chromatin in the light coloured nuclear juice, it contains generally 

 only one large nucleolus (caryosoma). 



The affected epithelial cells degenerate sooner or later as the 

 parasite feeds on them. After having had their form changed by 

 the growing parasite they finally perish. The cellular membrane 

 then alone surrounds the coccidia, which, at least in the species 

 sufficiently known, begin to propagate by an asexual process 

 (SCHIZOGONY) ; hereby the parasites themselves become schizonts, 

 as the initial stage is usually called. They differ from later stages 

 (sporonts), which resemble them in form, by the absence of granu- 

 lations in the plasma, as well as by the vesicular nucleus. The 

 form is not always alike, for in some cases, at least, many schizonts 

 assume a globular form. 



SCHIZOGONY (fig. 30) commences with a division of the nucleus, 

 which nevertheless takes place in different ways in the different 

 species, and finally leads to the formation of numerous daughter 

 nuclei which become smaller and smaller, and which collect beneath 

 the surface of the schizonts, but in some species collect only at one 

 half. A part of the protoplasm of the periphery now divides around 

 each daughter nucleus, the remaining part (residual body) being 

 left in the centre or on one side. The segments of the divided 

 plasm, each containing a nucleus, assume a fusiform shape and 

 become merozoits, which very soon gain their freedom and quit 

 the residual body (fig. 30, vii.). 



The merozoits move in a manner similar to that of the 

 sporozoites, from which they are, however, distinguished by a 

 somewhat different shape and the form of their nucleus. The 

 movements consist either of slow incurvations with subsequent 

 straightenings, or annular contractions along the entire extent of 

 the body ; in addition, there are gliding movements similar to 



