68 PRACTICAL PABASITOLOGY 



Order 1. Coccidia. 



The Coccides are typical cell parasites and, in particular, parasites 

 of the epithelial cells. The young free-living forms and the mature 

 male sex-forms are actively motile, the latter being furnished with 

 special organelles of movement in the shape of two flagella. In the 

 full-grown stage the parasites are either oval or round. The cuticle 

 is absent and there is no definite separation of the ecto- from the 

 endoplasm. The developmental cycle always includes an alternation 

 of generation, but it is never associated with a change of host. 

 Transmission to a fresh host is brought about by the agency of the 

 " oocysts," which are protected from external influences by a resistant 

 shell (fig. 20, xv). Within the oocyst, by repeated division of the 

 soft body, termed " sporogony," a number of " sporoblasts " are 

 formed (fig. 20, xvm), which, in their turn, surround themselves 

 with a secondary envelope or " sporocyst," and from which the 

 " sporozoites " finally proceed (fig. 20, xix). After transmission to 

 the intestine of a suitable host, the sporozoites emerge from their 

 covering (fig. 20, xx) and penetrate the epithelial cells (fig. 20, n), 

 where they develop into "schizonts" (fig. 20, in-iv). The schizonts 

 reproduce themselves by multiple division (fig. 20, ui-iv), without 

 previously encysting (fig. 20, v-vn). The products of this division 

 are termed " merozoites " (fig. 20, vm-x) ; they either develop 

 into schizonts and so increase the virulence of infection, or, if several 

 asexual cycles have followed one another, they become immature 

 sex individuals or " gametocytes " (fig. 20, xi a -xi b , xn -xn b ). The 

 female germ, or " macrogametocyte," develops into the mature 

 " macrogamete " by reduction of the nucleus without cell-division. 

 The male germ, or " microgametocyte," by a process of multiple 

 cell-division called " gamogony," forms numerous bi-flagellate 

 " microgametes," which emerge, leaving behind a large residual 

 body (fig. 20, xn c -xn e ). The fertilization of a macrogamete by a 

 microgamete (fig. 20, xm-xiv) is followed by the formation of the 

 " oocyst," which we took as the first stage in the developmental 

 cycle. The oocyst is formed by the secretion on the part of the 

 copula of a protective membrane, which hardens to form the oocystic 

 shell; or, where the macrogamete is already furnished with such 

 a membrane, the hole or "micropyle," through the microgamete 

 made its entrance, merely closes. 



The Coccides are parasitic in a large number of vertebrates, 

 molluscs, and articulates. They are found in the intestine and its 

 appendages as well as in the other excretory organs. The varieties 

 most suitable for demonstration purposes are those found in the gut 

 of Lithobius forficatus, in the kidney of Helix nemoralis, and in the 

 liver of rabbits. 





