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SCIENCE PROGRESS 



first six weeks of their life and if they can survive this period 

 unattacked they usually reach adult life. 



Fig. I. — Diagram of the life-cycle of Einieiia {Coccidium) avium. 



B-H illustrate the asexual reproduction (schizogony) of Eiiueria (Coccidiiiiii) avium ; i-L illustrate the forma- 

 tion of sexual forms (gametogony) of E. avium ; n-t show the formation of the oocysts (cysts) and 

 sporocysts (spores) of E. avium (sporogony) ; a, sporozoite or primary infecting germ which is 

 penetrating an epithelial cell of the duodenum of the host ; b, sporozoite curving on itself before 

 becoming rounded within the host-cell ; c, young, growing parasite ; d, fully grown parasite ; s, para- 

 site (schizont) with its nucleus divided (seen in transverse section) ; f, parasite forming merozoites, i.e. 

 daughter forms of the dividing parasite ; g, group of merozoites, arranged like the segments of an 

 orange ; H, free merozoites. i ^ , young female mother cell with coarse granules ; i (J , young male 

 mother cell with fine granules ', J ? , growing female mother cell ; J (J , young males beginning to form 

 in mother cell ; k ^ , female gamete that has formed a cyst-wall for itself, but left a thin spot for the 

 entry of the male ; k (J , fully formed males attached to their mother cell ; l, union of S and ^ : one 

 male only unites with the female, the others are excluded ; m, further stage in fertilisation ; n, fer- 

 tilised o5cyst (cyst) with its contents filling it ; o, oocyst (cyst) with contents forming a central mass : 

 many such cysts are seen in the droppings of infected grouse ; p, oocyst (cyst) showing first stage in 

 division into four ; q, oocyst with four daughter spores forming ; r, oocyst with four fully formed sporo- 

 cysts (spores) ; s, cyst with four sporocysts (spores), in each of which two sporozoites are formed ; 

 T, free sporocyst in which the sporozoites have taken up the most suitable position for emergence. 



The disease — we may call it Coccidiosis for short — caused 

 by this species of Coccidium {Eimeria avium) is brought about 

 in this way. The grouse moor is simply peppered over with 



