CHAPTER XIV. 



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, Leishmaniasis and trypanosomiasis 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 conditions 

 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, even Protozoa, are 

 subject to invasion by one type or other and adaptations are mani- 

 fold and varied in response to the necessary and often highly special- 

 ized conditions of their existence. 



In size the Sporozoa vary within wide limits; some are so small 

 that many of them may live together in a single mammalian erythro- 

 cyte (Theileria, Babesia) or in gland cells of different animals 

 (Microsporidia) . At the other extreme some forms of Gregarinida 

 (Porospora) grow to a length of 16 mm. In general they are larger 

 than flagellates, smaller than rhizopods and average about the 

 same size as the ciliates. 



Form also is variable but fairly consistent within the major 

 groups. Ameboid forms are characteristic of the Myxosporidia 

 and of the Plasmodiidae of the Hemosporidia. Coccidia for the 

 most part are spheroidal to ellipsoidal and gregarines elongate 

 ellipsoidal or ovoidal. Fantastic shapes are not uncommon, par- 

 ticularly amongst the Gregarinida— star shape in Astrocystella, 

 dagger shape, or branched forms in Aikinetocystis, etc. 



As with parasites generally, a necessary adaptation for the main- 

 tenance of species is the power of prolific multiplication. This is 

 realized by the universal method of reproduction by spore formation 

 to which the group owes its name. Such sporulation 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. 



