252 THE GROUSE IN HEALTH AND IN DISEASE 



flagella. Here they are attracted towards the macrogametes, 

 or female parasites, and commence to swarm round the aperture 

 in the cyst wall of the latter (Fig. 36, L). Before long, one micro- 

 gamete effects an entry, appears to bore its way into the female, 

 and is finally lost to view. Such is the process of fertilisation 

 as seen in the living organism. Then the aperture in the 

 macrogamete closes up whereby the other microgametes are 

 excluded, and the individuals thus shut out degenerate and die. 



After the microgamete has reached the interior of the 

 macrogamete, the male and female organisms become united, and 

 eventually develop into a zygote or oocyst (Fig. 36, N), which 

 passes into the gut, and is ejected with the excrement of the 

 Grouse. The oocyst is often called, in short, a cyst. 



The further development of the oocyst largely depends on 

 climatic conditions. Under the influence of warmth and moisture 

 its contents shrink away from the poles and become a rounded, 

 central mass (Fig. 36, O). This mass rapidly divides into two, 

 then four (Fig. 36, P) ; a wall is secreted round each, and thus, 

 in time, four sporocysts (Fig. 36, R) are produced within the 

 oocyst. Inside each sporocyst or spore two sporozoites 

 gradually develop (Fig. 36, S), and when the sporocyst (Fig. 36, 

 T) is ingested by a Grouse, the sporozoites creep out of the 

 sporocyst, which is softened by the digestive juices, and proceed 

 to attack the lining of the gut, producing thereby the primary 

 infection of the bird. 



A period of eight to ten days is required for a completion of 

 the life-cycle of the Coccidium from the time it is swallowed 

 by the Grouse till the new generation of cysts is deposited on 

 the moor in the droppings of the Grouse. Eight days old 

 Grouse chicks were the youngest naturally infected chicks 

 that have been observed. 



The effects of Coccidiosis on the Grouse may now be considered. 

 As already stated the chief external evidence of Coccidiosis is 

 the pale colour and great fluidity of the caecal (soft) droppings 

 of the bird, the pale tint being due to myriads of oocysts, and 



