CHAPTER IX. 



SPECIAL MORPHOLOGY AND TAXONOMY OF THE 

 SPOROZOA. 



Forms adapted to a parasitic mode of life are found in every main 

 group of the Protozoa and several highly pernicious human diseases 

 such as dysentery, Leishmaniases, and African sleeping sickness are 

 due to them. Such forms, however, may be regarded as having 

 arisen as casual parasites which owe their parasitic mode of life to 

 their original power to resist the digestive fluids and other condi- 

 tions of the animal body. Such adaptations are always possible 

 in normally free-living microorganisms subject to ingestion with 

 food and drink, 



Sporozoa are obligatory parasites and free-living forms are 

 unknown. Practically all kinds of animals are subject to invasion 

 by one type or other and adaptations are manifold and varied in 

 response to the necessary and often highly specialized conditions 

 of their existence. As with parasites generally, a necessary adap- 

 tation for the maintenance of species is the power of prolific multi- 

 plication. This is realized by the universal method of reproduction 

 by spore formation to which the group owes its name. Such sporu- 

 lation may occur as multiple reproduction of vegetative individuals 

 without sexual processes or it may follow as a result of fertilization. 

 Asexual and sexual processes give rise to typical alternation of 

 generations in the majority of forms and complicated life histories 

 result. 



Asexual reproduction may occur by equal division {e. g., Ophryo- 

 cystis, Babesia, etc.) ; by budding which may be exogenous (Myxo- 

 sporidia) or endogenous (as in the gregarines Schizocystis and 

 Eleutheroschton) , or by multiple division (Coccidiomorpha) . 

 Reproduction following fertilization always involves the formation 

 and the permanent fusion of gametes. These may be isogamous or 

 anisogamous and dimorphic gametes as different as are eggs and 

 spermatozoa of the Metazoa are characteristic of the Coccidia and 

 Hsemosporidia. Sexual processes of peculiar type and regarded as 

 self fertilization or autogamy are characteristic of the Cnidosporidia 

 where such processes with resulting sporulation, take place in endo- 

 genous buds. 



Sporulation following fertilization in the majority of forms, 

 involves adaptations for preservation of the species during exposure 

 to the conditions external to the definitive host. Such spores are 



