138 THE ANIMAL PARASITES OF MAN 



their presence in the latter situation is probably only secondary, 

 that is, they have only reached it from the epithelium of the affected 

 organs. 



The size of the Coccidiidea, corresponding as a rule to the capacity 

 of their habitat, is usually small, but there are said to be species 

 that attain a diameter of i mm. Their form 1 is globular, oval, or 

 elliptical. External appendages are lacking, at least during the trophic 

 or vegetative period of their life, which is spent in epithelial cells, 

 within which they increase in size. Frequently one only is present 

 in each cell, but more can occur. The body substance is composed 

 of a more or less finely granular or distinctly alveolar protoplasm 

 which exhibits no differentiation into ecto- and endoplasm. All 

 species possess a nucleus that enlarges with their growth ; some- 

 times it only shows through the cytoplasm as a lighter spot, or may 

 even be quite concealed. It is vesicular, and besides containing very 

 delicate threads of chromatin in the clear nucleoplasm, it contains 

 generally only one large karyosome. 



- : The infected epithelial cells degenerate sooner or later as the 

 parasite feeds on them (fig. 67, n-iv). After their form has been 

 changed by the action of the growing parasite, they finally perish. 

 The cell membrane then alone surrounds the coccidia, which, at 

 least in the species sufficiently known, begin to propagate by an 

 asexual process (schizogony), the parasites themselves becoming 

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

 stages (sporonts or gametocytes), which resemble them in form, by 

 the absence of granulations in the cytoplasm, as well as by the 

 vesicular nucleus. The form is not always the same, for in some 

 cases, at least, many schizonts assume a globular form. 



Schizogony (fig. 67, v-vn) commences with a division of the 

 nucleus, which takes place in different ways in the various species. 

 This finally leads to the formation of numerous daughter nuclei 

 which become smaller and smaller, and which collect beneath 

 the surface of the schizonts. In some species the daughter nuclei 

 collect only in one half of the schizont. 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 cytoplasm, each containing 

 a nucleus, assume a fusiform shape and become merozoites, which 

 very soon become free (fig. 67, vin) and leave the residual body. 

 They are distinguishable from the very similar sporozoites (fig. 67, i), 

 as the merozoites possess a karyosome. 



1 The life-cycle given here is based on that of Eimeria (Coccidium) schubergi, after 

 Schaudinn (1900). See " Untersuchungen liber den Generationswechsel bei Coccidien," ZooL 

 fahrb., Abt. f. Anat., xiii, pp. 197-292, 4 plates. 



