CHAPTER V 



THE SPOROZOA 



The Sporozoa are unicellular animal parasites living in the cells, 

 tissues, and cavities of various hosts and, as the name indicates, char- 

 acterized by reproduction through spore-formation. If we except 

 the bacteria, they are the most widely distributed of all parasites, and 

 are found in every class of animals, frequently in Vermes, Arthrop- 

 oda, Mollusca, and Vertebrata, rarely in Protozoa, Ccelenterata, and 

 Echinodermata. They may infest the alimentary tract, and all 



Fig. 77- — The vegetative phase in the life-history of a 

 gregarine (schematic). [WASIELEWSKY.] 

 The young sporozoite (A), liberated in the intestine, 

 enters an epithelial cell (B), where as an intra-celliilar 

 parasite (p) it grows at the expense of the cell-contents, 

 often forcing the nucleus («) to a corner of the cell. It 

 finally grows through the cell-wall (C) and ultimately 

 drops into the lumen of the organ as a sporont (D). 



D 



of the connecting organs and ducts; the kidneys and their ducts; 

 the blood-vessels and the blood ; the muscles and connective tissues ; 

 while even the skin is not exempted. In most instances they are harm- 

 less, but they may produce morbid and even fatal results, either in- 

 directly, by increasing to such numbers that the lymph-spaces and 

 cavities are filled with them, thus preventing nutrition of the cells and 

 tissues, or directly, by causing atrophy and death of the cells in which 

 they live. They are usually taken into the system in the spore-stage 

 with the food of their host, although infection may take place through 

 the gills or lungs, or even by inoculation from insects. The spore- 

 membranes are soon dissolved by the fluids of the host, and one or 

 more germs are thus liberated. These germs, the sporozoites, then 



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