dysentery, an intestinal disease of man, characterized by alternate 

 diarrhoea and constipation, intestinal catarrh, and sometimes 

 ulceration of the wall. The organism occurs in the pig, with similar 

 forms in amphibia and annulates. Opalina ranarum, parasitic in 

 the rectum of frogs, resembles Balantidium, but is multinucleate. 



The Sporozoa are entirely parasitic. Their chief feature is 

 reduction of motile structures and, in many cases at least, develop- 

 ment of a more resistant cell membrane. Of prime significance, 

 however, is the adaptation of the life cycle to rapid reproduction, 

 attained by means of multiple cell division or "sporulation". 



The group contains a number of early recognized forms known 

 as Gregarinida, sometimes as "gregarine worms", of which some 

 are simple spindle-shaped or elongated organisms living in the body- 

 cavities of invertebrates, e.g., Monocystis in the seminal vesicles of 

 the earthworm, while others show a transverse division of the cell, 

 differentiating a head lobe or epimerite which serves for attach- 

 ment and may be lacking in some stages, e.g., gregarines of the 

 digestive tract of insects, notably Gregarina blattarum of the intes- 

 tine of the cockroach. 



Coccidium types or Coccidia are intracellular parasites of 

 the epithelial cells of various animals. Eimeria stiedae ( = Coccidium 

 cuniculi) of the liver of the rabbit was one of the first studied. 

 Eimeria schubergi from the intestinal epithelium of the centipede 

 LitJwbius is commonly taken as the type. The organism penetrates 

 the epithelial cell in the sporozoite stage. It reaches maturity 

 at the expense of the host cell. There are two main phases or cycles 

 in the life history, one adapted for distribution of the parasite in 

 cells of the host, the other for transmission to another host animal 

 of the same species. The processes are as follows: 



(a) Re-infection of host. The adult cell undergoes multiple 

 division into merozoites, each of which gains access to a new 

 epithelial cell. The process is purely asexual and is known as 

 schizogony. 



(b) Preliminary stages to transmission. After the period of 

 schizogony the adult cells become differentiated into sperm and 

 egg mother cells. The latter becomes an oocyte or macrogamete 

 by extrusion of a certain amount of the chromatin. The former 

 undergoes multiple division resulting in the formation of a large 

 number of bi-fiagellate sperms or microgametes. The fertiliza- 

 tion is followed by membrane consolidation around the egg which 

 thus becomes an oocyst. There is then an internal division into 

 four spores each enclosed by a thick encystment membrane. The 

 protoplasm of each spore undergoes division into two sickle-shaped 

 sporozoites. The development is now finished unless the liberated 



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