128 SOME MINUTE ANIMAL PARASITES 



(Fig. 28, N). The fertilized oocyst (encysted zygote 

 or cyst) now enters upon a series of changes leading 

 to spore-formation, the stages in the life-history being 

 known as sporogony (Fig. 28, N-T). 



When the stage of oocyst formation is reached, 

 the perpetuation of the parasite is ensured, and there 

 is the possibility of the recovery of the host, for if 

 the oocysts are discharged from the body and there 

 are no young merozoites to continue the growth, the 

 injured gut epithelium may be able to form again, 

 and then the bird recovers. The systematic examina- 

 tion of the droppings of the bird thus can be used as 

 a rough index of the possibility of the recovery or 

 otherwise of the bird. This matter will be more 

 fully discussed later. Examination of a minute 

 portion of faecal matter when freshly voided usually 

 shows all the oocysts with their contents filling them 

 entirely (Figs. 28, N ; 29, A). After a short time the 

 contents of the cyst begin to contract, and gradually 

 a spherical mass is formed within each oocyst, a 

 space being left at either pole (Figs. 28, O ; 29, B). 

 Cysts two to three days old often show complete 

 development, though the stage reached depends 

 partly on favourable conditions. Should the condi- 

 tions be of the best, the nucleus of the oocyst divides 

 into two, and this division is followed with extra- 

 ordinary rapidity by another, so that the oocyst has 

 four nuclei (Figs. 28, P ; 29, C). The proto- 

 plasm separates at the same time into four ball-like 

 masses (Figs. 28, Q ; 29, D), so that the oocyst 

 contains four spheres. These soon elongate and 

 become oval (Figs. 28, R ; 29, E) and quickly 



