CHAPTER XLIII 



SPOROZOA 



THE Sporozoa stand alone among the protozoa, in that all 

 the species are parasites. Many are harmless commensals, but a 

 considerable number are pathogenic. The sporozoan cell contains 

 typically a single nucleus, except in the Myxosporidia which are 

 multinucleate. Food is taken in by diffusion through the plasma 

 wall. Gastric and contractile vacuoles are present. The adult 

 form is non-motile; the young forms are frequently actively 

 motile, either ameboid or flagellate. In most of the Sporozoa 

 the differentiation of the protoplasm into ectoplasm and endo- 

 plasm can be clearly made out The reproduction of the Sporozoa 

 is the principal character which differentiates this group from 

 others. Spores are always produced in those forms in which the 

 complete life-history is known. The details of spore-formation 

 vary greatly in the different forms, but the essentials are the same. 



The cell as a whole, in most forms, divides to form archispores 

 or sporoblasts ; each of the archispores forms spores, and each spore 

 then produces one or more sporozoites. Many forms show addi- 

 tional methods of reproduction. Formation of sex cells or gametes, 

 with fusion of like or unlike cells, takes place in many forms, and 

 serves to further complicate the life-history. 



Blood-smears may be stained by one of the Romanowsky 

 stains or by Wright's method to demonstrate the protozoa of this 

 group. Considerable care must be exercised in the examination 

 of such blood mounts not to confuse the normal blood contents, 

 such as blood-platelets, with developmental stages of the protozoa. 



The class Sporozoa contains many families and genera; only 

 a few of the latter contain species that are of economic importance. 

 The following artificial key will assist in differentiating the various 

 genera. 



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