CHAPTER XIV 

 THE SPOROZOA : I. THE GREGARINES AND COCCIDIA 



UNDER the common denomination Sporozoa are grouped together 

 a great number of parasitic organisms extremely varied in form, 

 structure, habitat, and life-history, but of which the most general 

 though not invariable characteristic is that the propagation of the 

 parasite from one host to another is effected by means of spores, 

 in the primary sense of the word (see p. 165, footnote) that is to 

 say, resistant seed-like bodies within which one or more parasitic 

 germs are protected by a firm envelope or capsule, whereby they are 

 enabled to resist the vicissitudes of the outer world until they pass, 

 in one way or another, into the body of a suitable host ; when this 

 end is attained, the spore germinates that is to say, the contained 

 organisms are set free and a fresh infection is started. 



It is very obvious that propagation by means of resistant spores 

 is a character very inadequate for diagnosing an extensive group 

 of Protozoa. In the first place, many organisms, parasitic 

 or free-living, which are not included in the class Sporozoa, are 

 propagated by means of resistant spores. In the second place, 

 many forms included in the Sporozoa do not produce resistant spores, 

 being propagated by methods which render any such phase un- 

 necessary. The class therefore ceases to be amenable to strict 

 verbal definitions, and it is not surprising that the limits 

 assigned to it have varied at different times, and are even now 

 debated. The class Sporozoa was originally founded by Leuckart 

 to comprise two closely allied orders the Gregarines and the 

 Coccidia. To this nucleus other groups were added, in particular 

 the various forms termed vaguely " psorosperms "* a word 

 coined originally by Johannes Miiller to denote the spores of the 

 Myxosporidia, but soon extended to other parasitic organisms. 

 Thus " Sporozoa " and " psorosperms " became practically 

 synonymous terms, and the class to which these names were 

 applied became a most heterogeneous assemblage of organisms 



* From the Greek ^cipa, mange, and <nrep/j.a, a seed, on account of the 

 sores and ulcers of the skin of fishes produced by Myxosporidia, and the resemblance 

 of their spores to little seeds. 



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