Forms typically characterised by having two kinds of cysts, a zoocyst in which the organism undergoes division into spores either flagellulae or amoebulae, a sporocyst in which it becomes a resting-spore or chlamydospore. Zopf makes two subdivisions, M. zoosporeae and M. azoosporeae1.

M. zoosporeae. The zoocyst gives origin to flagellulae s. zoospores. There are three families.

The first, Pseudosporeae, is characterised by the fact that the chlamydospore is formed in a sporocyst. There are four genera. Colpodella pugnax is sickle-shaped, with a single cilium, nucleus and contractile vacuole. It perforates the membrane of the green Flagellate Chlamydomonas pulvisculus and sucks out its contents. Next it comes to rest, becomes globular, forms a double membrane, an outer thick, and an inner thin; then segments into a number of zoospores which are set free by the bursting of the thick membrane, the protrusion and gelatinisation of the thin. When it passes into a chlamydospore it becomes globular, secretes a membrane and then contracts into a small globular or ellipsoidal body. The genus Pseudospora differs from Colpodella in that the zoospore passes into an Actinop/irys-like Amoeba. Ps. aculeata is parasitic in the cells of the algal Oedogonium; Ps. parasitica in those of Spyrogyra; Ps. Bacillariacearum in Diatoms; Ps. maligna in the protonemata of the Moss Hypnum. The resting-spore is known in the two first named. The ingesta are expelled within the cyst before the spore membrane is formed. Proto-monas is distinguished from the foregoing by forming fusion-plasmodia. P. amyli is an inhabitant of stagnant waters, and lives upon starch grains.

The zoospore is biciliate, the two cilia being at one or at opposite ends of the body. It passes into an Actinoplirys-like Amoeba, which as it grows loses the power of emitting pseudopodia; it then forms a cyst and segments into zoospores. Or several spores may fuse into a plasmodium round a starch grain. The plasmodium does not emit pseudopodia, and finally secretes a membrane. It then segments into zoospores, or before it does so, it may escape from the cyst and creep about by means of long pseudopodia. The resting-spore is ellipsoidal or globular with a thick cyst which has minute internal tubercles. P. Spirogyrae is parasitic in Spirogyra and Zygnema. The zoospore is uni-ciliate; it forms amoebae or plasmodia with blunt pseudopodia. The resting-spore behaves like that of Pseudospora. P.Huxleyi is marine, and lives upon Diatoms. The genus Diplophysalis is characterised by the fact that the restingspore has a double cyst. D. Stagnalis and D. Nitellarum live in the cells of Chara and Nitella. The inner cyst-membrane to the resting-spore is spinose in the former, smooth in the latter.

D. Volvocis feeds on the zooids of Volvox.

1 The following epitome is made from Zopf's article in the 'Encyclopaedic der Wissenschaften,' quoted infra.

The second family of M. zoosporeae is the Gymnococcaceae. The resting-spore has as usual a membrane but no cyst, and the ingesta are expelled before its formation. Gymnococcus forms its zoospores in a cyst; G. Fockei is parasitic in Diatoms; G.perniciosus in the cells of C/adophora, G. spermophilus in the spores of the blue-green Alga Cylindrospermum. Aphilidium deformans inhabits the cells of the Alga Coleochaete; its zoospores have no cysts. Pseudosporidium lives in cultures of Algae. The zoospore gives origin to a slug-like Amoeba, which may form a resting or hypno-cyst and become free again. It ends by becoming globular, secreting a membrane, perforated and furnished with an operculum at one spot where the zoospores, to which it gives rise, escape. Proto7nyxa aurantiaca is marine, and was found by Haeckel on the shell of a Spirula in the Canary Islands. It forms a laminated globular cyst .12 - .2 mm. in diameter, the orange-coloured contents of which segment into some hundreds of uni-ciliate pyriform zoospores. The latter become amoeboid; some of the Amoebae fuse into an orange-coloured plasmodium with reticulate pseudopodia which feeds on Diatoms and Peridinidae, and eventually encysts again.

Haeckel found no nucleus.

The third family of M. zoosporeae is the Plasmodiophoreae. Its members are parasitic in the cells of the roots of plants. The amoeba breaks up within the cells into minute zoospores and there is no cyst. Plasmodiophora Brassicae infests Cruciferae, especially species of Brassica; Tetramyxa parasitica various water plants. The latter is peculiar in that the Amoeba first divides into cells, and the latter in turn each into four spores which remain united. It is possible that the Amoeba is a plasmodium.

M. azoosporeae. The zoocyst gives origin to amoebulae. There are three families.

The first is the Vampyrellaceae, all aquatic and feeding on living or dead Algae, Fungi, Protozoa, etc. Vampyrellidium vagans is aberrant. It infests Oscilla-toriae, Saprolegniae, etc, and when full fed becomes globular or oval and develops a thin or thick membrane, in either case escaping as a single Amoeba. Zopf places here with some doubt Spirophora (Amoeba) radiosa which feeds on Scyto-nemeae. When floating it is globular, when creeping flattened. Its pseudopodia are long, with a tendency to twist terminally into spirals; they vibrate to and fro (see Butschli, Z. W. Z. xxx. p. 271). It passes into a globular resting-spore, after ejecting all foreign bodies. The spore gives rise to a single Amoeba. Haplococcus reticulatus lives between the muscle-fibres of animals, especially swine. Its zoocyst is globular with three or several round papilliform spots from which the amoebulae (6-15) escape. The resting-spore is round or tetrahedral, but has no cyst. The genus Vampyrella has seven or eight species, one of which, V. Gomphonematis, is marine, and feeds on the branched Diatom Gomphonema. The other species feed principally on various freshwater Algae either engulfing Diatoms, Desmids, or sucking out the cell-contents of filamentous Algae by pseudopodia emitted from a stout process which perforates the cell membrane.