3. Order Haplosporidia. The true Haplosporidia are probably Microsporidia whose spores do not produce a polar capsule. They occur in the tissues of animals, chiefly invertebrates; distinctly pathogenic forms have not been found. Important types : Haplo sporidium (in various worms), Ichthyosporidium (in marine fishes, such as Crenilabrus).
Many forms of "Sporozoa" have been included in this group about whose developmental history nothing exact is known; for example, Rhinosporidium seeberi, which produces tumours in the mucous membrane of the nose in man. Some of these forms be long perhaps to the Haplosporidia; others, however, to the fungi.
4. Order Actinomyxidia. The vegetative stages of these pro tozoans are not yet well known. Spore-formation probably fol lows a course broadly the same as that described for the Haplo sporidia; there is for instance a paedogamous fertilization. The spores are very complex, of triradiate symmetry and containing three polar capsules. A very peculiar character is the way the spore-shell, in some species, is formed not around the amoeboid germ but quite apart from it, the germ only slipping into the shell when the latter is complete. Almost all known Actinomyxidia live in the Tubificidae (relatives of the earthworm) and are more or less harmless. Important types :—Sphaeroactinomyxon, Tri actinomyxon.
5. Order Sarcosporidia. It is still doubtful if these protozoans are related to the Neosporidia or not, their life-cycle being as yet imperfectly known. The vegetative individuals or "utricles" are usually oval or spindle-shaped multinucleate clumps, which may attain to a considerable size—as much as two inches long. The Sarcosporidia are muscle-parasites of vertebrates, chiefly mam mals; the utricle in its young stages lies in the muscle-fibres, the adult utricle lies between them. Some species are markedly pathogenic, for example Sarcocystis miescheriana of the pig, which may lead to laming of the hind legs. It is noteworthy that it was in the Sarcosporidia that toxins were first recognized. Important .
types : Sarcocystis miescheriana (pig), Sarcocystis tenella (sheep). 5. Class Ciliophora. Protozoa that move by means of numer ous cilia ; free-living or parasitic.
I. Order Opalinida. Uniformly ciliate Protozoa, usually multi nucleate, whose nuclei (in contradistinction to those of the Ciliata) are all alike (fig. 24). Harmless intestinal parasites, feeding osmotically. Reproduction by simple fission; fertilization is by copulation, this being a second distinction from the Ciliata. Important types:—Opaiina ranarum (rectum of the grass frog).
2. Order Ciliata. (Infusoria.) More or less uniformly ciliate, nuclei varying from two to many, always of two kinds, macro and micronuclei (fig. 4). Only the latter kind can divide mitoti cally, the macronuclei degenerate at conjugation. Most ciliates are free-living and take in food by gulping it or whirling it in. The same applies to most of the parasitical forms—the greater part of which are external or intestinal parasites ; but there are also parasitic forms that feed osmotically. Alternation of hosts does not occur. These organisms are unicellular throughout but some times form colonies. Reproduction by simple transverse fission or (more rarely) by multiple division in a cyst. Fertilization by
conjugation.
The Ciliata are divided according to the arrangement of the cilia and other characteristics into numerous groups which need not be further discussed here. Important types :—Paramaecium (fig. 4), Stylonychia, V orticella, Stentor (fig. 3), Chilodon (fig. 8), Didinium (fig. 5) (all free-living pond-dwellers), Tintinnus (and related marine plankton forms, with cup- or jug-shaped shells), I chthyophthirius multifiliis (parasitic on the skins of fresh-water fish, trout, etc. ; pathogenic), Balantidium coli (gut of man and of the pig; possibly not quite harmless), Ophryoscolex, Ento dinium and related forms (characterized by meagre ciliation and possession of a strong cellulose armour; enormously abundant in the stomachs of almost all the hoofed animals—cattle, sheep, pigs, horses, antelopes, etc.), probably symbionts like the Tri chonymphidae, but not indispensable.