(d) Sub-order Tripylea. Central capsule with three complex apertures. Skeleton very highly developed. Important types :— Aulacantha, Coelacantha.
6. Order Mycetozoa, also known as slime moulds but are not true fungi. (a) True Mycetozoa (Myxogasteres). These are Rhizopoda whose vegetative stage, the so-called plasmodium, is a gigantic Amoeba with thousands of nuclei. A contracted plas modium of Fuligo varians, "flowers of tan," can be as large as a man's fist. These Amoebae are not compact, but form a peculiar net in whose meshes the endoplasm flows back and forth. The creeping forward movement of the plasmodium is caused by the fact that the plasma streams longer in one direction than in the other. The plasmodia live in moist earth, dung and rotten wood and they live partly on particles of decay ing vegetable matter and partly on bacteria. The plasmodia cannot as a rule multiply vegetatively, they can only increase in siae and in number of nuclei. When the plasmodium dries it changes to a number of thickly crowded multicellular cysts and is then known as a sclerotium. When food runs short the plasmodium forms fruiting bodies, the protoplasm collecting itself into little clumps at various parts of the net; from every clump a stalked ball-shaped body grows up; this fruiting structure is surrounded by a firm membrane and contains a great number of unicellular cysts or spores. At the formation of the fruit-bodies only a portion of the protoplasm is used up in the formation of spores; the rest goes to the making of the stalk, fruit-body membrane and fibres of a particular kind called elaters, which lie between the spores. The spores can stand drought, but as soon as they come in contact with water uniflagellate swarm-spores escape from them which either mate immediately or change first into Amoebae, losing their flagellae. The amoeboid zygote then grows straight on into a new plasmodium. Important types : Didymium nigripes, on dung and garden soil; Fuligo varians, on tanner's bark.
(b) The Acrasiaeae are also courted with the Mycetozoa although in no way related to them. The vegetative stage is a uninucleate amoeba multiplying by fission; on the formation of fruit-bodies many thousands of these organisms come together, and gradually build ball-shaped fruit-bodies which are often stalked; some of the amoebae are transformed into stalk cells, others into the membrane, the greater number form uninucleate spores. Important type : Dictyostelium mucoroides.
(c) Perhaps other plasmodial Rhizopoda such as Labyrinthula, Leptomyxa and such forms should belong to the Mycetozoa but we know as yet little of their life cycles. (See FUNGI.) 3. Class Telosporidia.—A small group of exclusively para sitic Protozoa whose zygotes break up inside a membrane into numerous sporozoites. Nutrition purely osmotic. Chromosome reduction at the first division of the zygote nucleus.
I. Order Coccidiomorpha. Telosporidia in which the vegetative individual dispenses with every cell organoid ; they flourish inside cells and reproduce by multiple division.
(a) Sub-order Coccidia. From the sporozoites or merozoites arise the vegetative individuals or macrogametocytes and micro gametocytes, which give rise to a large number of gametes. The zygote breaks up inside its membrane into several sporoblasts which themselves grow an enveloping membrane to become spores and whose protoplasm breaks up into sporozoites. Coccidians are found in many different groups of animals, including man, and in the most diverse tissues, very often in gut cells ; some cause dangerous diseases, as Eimeria stiedae, a serious intestinal com plaint of the rabbit ; others are practically innocuous. Important types: Eimeria stzedae (rabbit), Eimeria schubergi (intestine of Lithobius forficatus, a centipede), Aggregata eberthi (intestine of Sepia and crabs).
One family of the Coccidia, the Haemogregarinae, provides the transition to the Haemosporideae. The Haemogregarinae are dis tinguished from other coccidians, with which the resemblance is otherwise very close, in that the zygote, called the ookinete because it is at first motile, is enveloped in a membrane; the sporozoites have no spore membrane. The haemogregarines are parasites of the red blood corpuscles of reptiles, frogs and mammals; some of them have a similar alternation of host to that of the Haemo sporideae; some are pathogenic, such as Hepatozoon perniciosum, of the wild rat. Important types : Karyolysus (chief host, lizards, intermediate host, mites), Hepatozoon (rats).