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SPOROZOA
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SPOROZOA , a large and most important See also:section of the See also:Protozoa, all the members of which are exclusively parasitic in See also:habitat. They are of extremely widespread occurrence; there is hardly one of the See also:chief classes of animals which does not furnish hosts for these parasites, scarcely one of the See also:common tissues or See also:organs of the Metazoan See also:body which may not be liable to infection. Sporozoa differ greatly as regards the effects which they produce upon their hosts. In many, perhaps in most, cases the See also:general See also:health of the infected See also:animal seems to be unimpaired, even though the parasites may be fairly abundant. Some, however,give rise to dangerous or fatal diseases, while others may cause ravaging epidemics; instances of these are given under the various orders. Correlated with the mode of See also:life are the two features characteristic of all Sporozoa: (a) They absorb only fluid nutriment, osmotically, and so lack any organs for ingesting and digesting solid See also:food; and (b) they reproduce by sporulation, i.e. the formation of See also:minute germs, which are in most instances very numerous and are often enclosed in See also:firm protective envelopes or cases, each See also:case with its contents forming a spore. In addition, the See also:great See also:majority have also another method of See also:reproduction, for increasing the number of the parasites in any individual See also:host; this is distinguished as multiplicative or endogenous reproduction, from the propagative or exogenous method (by means of the resistant spores), which serves for the infection of fresh hosts and secures the dissemination and survival of the See also:species. Further, most if not all forms of Sporozoa undergo sexual conjugation at some See also:period or other of the life-See also:cycle. Beyond this, however, it is impossible to generalize. In response to the exceeding diversity of habitat and of the conditions of life, the parasites exhibit manifold and widely-different types of See also:form, organization and life-See also:history. The recognition of this fact is expressed, at the See also:present See also:day, by the See also:division of the Sporozoa into several well-defined orders, which are grouped in two See also:main divisions, each containing more or less closely related forms. One of these See also:groups consists of the See also:Gregarines, See also:Coccidia and See also:Haemosporidia (qq.v.). The other comprises the Myxosporidia, Actinomyxidia, Sarcosporidia and Haplosporidia, the parasites included in the last named See also:order being of comparatively See also:simple structure, and probably near the See also:base of this section. There are, in addition, various other forms (Sero- and Exo-sporidia), also See also:primitive in See also:character, but which are as yet too insufficiently known for it to be certain whether they are of distinct ordinal See also:rank, or should be placed with the Haplosporidia. The nomenclature assigned to these two See also:principal divisions of the Sporozoa by different writers has varied according to the particular character on which they have primarily based the arrangement. Of See also:late years, the terms Telosporidia and Neosporidia, proposed by F. Schaudinn (igoo), have been most in favour. In the Telosporidia (comprising the Gregarines, Coccidia and Haemosporidia), sporulation does not begin until the See also:close of the vegetative or trophic period, i.e. until growth has ceased; in the Neosporidia (including the remaining orders) growth and sporulation go on coincidently. Recently, however, considerable doubt has been thrown upon the general occurrence of this latter See also:condition in certain Myxosporidia (Microsporidia); and the present writer adopts as preferable, therefore, the terms See also:Ectospora and See also:Endospora (qq.v.), invented by E. Metschnikoff and made use of by F. Mesnil (1899), which indicate a universal distinction between the two groups in their manner of sporulation. This distinction is probably the most fundamental one, and itself supports a conclusion which is, on other grounds, becoming more and more likely, namely, that these two divisions are not related phylogenetically; but have, on the contrary, a radically different origin. In other words, under the heading Sporozoa, as at present used, are included two entirely See also:independent See also:series of Protozoan parasites; the general resemblances which these exhibit are due to convergence brought about by their specialized mode of life. The most See also:recent and comprehensive See also:account of the See also:group is that by E. A. Minchin (in Lankester's See also:Treatise on See also:Zoology, pt. i., See also:London, 1903), to which the present writer is much indebted; another useful treatise is that of F. Doflein, See also:Die Protozoen als Parasiten u. Kranhheitserreger (G. See also:Fischer, See also:Jena, 1901). Earlier accounts are those of M. Liihe, Ergebnisse der neuren Sporozoenforschung (Jena, 1900); Wasielewski, Sporozoenhunde (Jena, 1896); Y. Delage and E. Herouard in Traite de zoologie See also:concrete, pt. i., See also:Paris, 1896) ; E. R. Lankester, See also:art. " Protozoa " in Ency. Brit. 9th ed. (1886), and 0. Butschli in See also:Bronn's Klassen u. Ordnungen See also:des Thierreichs, I. i. (1882). There is a systematic enumeration of the group by A. Labbe in Des Thierreich, 5. (See also:Berlin, 1899) ; and the See also:classification and phylogeny are considered by E. Mesnil (See also:Soc. Biol., vol. jub. p. 258, Paris, 1899), and by H. Crawley in Amer. Nat. (1905), xxxix. 607. (H. M. Additional information and CommentsThere are no comments yet for this article.
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