II] HAEMOSPORIDIA 45 



usually eight falciform young. All the Gregarinidea in the adult 

 stage are at least partly free from the cells of the host. The 

 Coccidea consist of forms in which the trophozoite remains com- 

 pletely immersed in the cells of the host. The adults divide into 

 sickle-shaped young which escape and enter other cells; after a time 

 they become converted into male and female forms, the so-called 

 microgametocytes and megagametocytes. In the former the 

 nucleus breaks up into minute rod-like portions which, acquire flagella 

 and become free in the alimentary canal of the host. The mega- 

 gametocyte rounds itself off and forms the female gamete, drops out 

 of the cell in which it is, into the alimentary canal and is here 

 fertilised. The zygote develops into a sporangium, the contents 

 of which divide into several spores and each spore gives rise to 

 several amoeboid young. 



The Haemosporidia differ from the two foregoing familes in 

 the following points. 



(1) The adult inhabits the cells of the blood of the host, not of 

 its alimentary canal. 



(2) The adult has its cortical layer badly or not at all developed, 

 so that it resembles Amoeba in its power of changing its shape. 

 The Haemosporidia agree with the Coccidea in possessing gametes 

 of two sizes, but the sexual phase is usually passed in the interior 

 of an insect, whilst the stage of asexual multiplication is passed in 

 the blood of a Vertebrate. Laverania malariae is the cause of 

 ague or malarial fever. The adult lives in a red blood corpuscle 

 (see p. 433) and eats it out, transforming the red haemoglobin into 

 black pigment (melanin). The parasite then divides into sickle- 

 shaped young (as in the Coccidea) which escape into the blood and 

 cause an onset of fever. They soon enter and attack other blood- 

 cells. If the blood of a patient is sucked by the mosquito 

 Anopheles , the parasite becomes changed into the sexual form in 

 the stomach of the insect. As in Coccidea megagametocytes and 

 microgametocytes are formed, and the small male gametes fertilise 

 the large rounded female gametes. The zygotes force their way 

 through the wall of the insect's stomach into its blood, and there 

 become surrounded with a cyst wall. The contents divide into 

 sickle-shaped young and these migrate into the salivary glands of 

 the Mosquito and await their opportunity of entering the wound 

 which the Mosquito makes on the next person it bites. Piroplasma 

 is a similar parasite in the blood of cattle where it causes red-water 

 fever. It is transmitted from one beast to another by a tick. ' 



