INTRODUCTION. 5 



started. The mode of transfer of the spores is usually con- 

 tamuiative, that is to say, the spores are ingested with the food 

 that has been contaminated with faeces in which the spores 

 have been passed. In some forms, however, where the parasite 

 passes part of its hfe- cycle in the blood of one host and part 

 in the body of a widely different host, the sporozoite is not 

 enclosed within a definite membrane or cyst, and the method 

 of transfer is inoculative. 



The method of nutrition is by osmosis only. The organism 

 does not possess pseudopodia, flagella or ciHa for the purpose 

 of food-capture. Where the organism is amoeboid, its pseudo- 

 podia are for the purpose of increasing the extent of the body- 

 surface for absorption, rather than for the ingestion of solid 

 particles of food. The parasite may invade the cells (cytozoic), 

 or spaces between the cells {histozoic),ov may hve in the lumen 

 of the ahmentary canal or other cavities in the body of the host 

 (coelozoic). The food material absorbed from the host will 

 thus be dissolved cytoplasm, tissue fluid, body fluid, or digested 

 food material from the ahmentary canal of the host. The 

 Spoeozoa are parasitic in animals of almost every phylum 

 from Protozoa to Chordata, and while many of them have 

 come to be tolerated, others are responsible for causing 

 deadly disease and heavy mortahty among the hosts. In 

 accordance with thek widely varied habitat, they show 

 manifold adaptations suiting them to the highly speciahzed 

 conditions of their existence. 



Form and Structure. — The Sporozoa show a more or less 

 comphcated hfe-history, consisting of various stages. The 

 starting point is the minute germ or sporozoite, which may have 

 one of two forms. In Amcebosporidia it is a minute amoeboid 

 organism termed an amoebula ; in the Telosporidia it is 

 more definite in form, being a rod-like or sickle-shaped body 

 (" falciform body ") which is capable of twisting or bending 

 movements and progresses by ghding, and is described as 

 a gregarmula. The sporozoite, after being set free in the body 

 of the new host, nourishes itself and grows, often to a relatively 

 large size, at the expense of the host. This is the trophic 

 phase, and the organism during this phase is described as the 

 trophozoite. The trophozoite absorbs nourishment in the 

 fluid state, and does not exhibit any organs of locomotion, 

 ingestion or digestion ; neither food- vacuoles nor contractile 

 vacuoles are present. The parasite has usually a fixed form 

 with definite contours, being limited externally by a cuticle 

 of greater or less thickness, and may either grow inside a host 

 cell or be attached to a cell of the host by a special organ of 

 fixation known as an epimerite. The ectoplasm is in certain 

 groups differentiated into three layers, known as epicyte, 

 sarcocyte, and myocyte, the latter being composed of myonemes 



