5. Proteomyxa

Sarcodina without a clear ectoplasm, whose active forms are amoeboid or flagellate, or pass from the latter form to the former; multiplying chiefly, if not exclusively, by brood-formation in a cyst. No complete cell-pairing (syngamy) known, though the cytoplasms may unite into plasmodia; pseudopodia of the amoeboid forms usually radiate or filose, but without axial filaments. Saprophytic or parasitic in living animals or plants.

This group is a sort of lumber-room for forms which it is hard to place under Rhizopoda or Flagellata, and which produce simple cysts for reproduction, not fructifications like the Mycetozoa. The cyst may be formed for protection under drought ("hypnocyst"), or as a preliminary to spore-formation ("sporocyst"). The latter may have a simple wall (simple sporocyst), or else two or three formed in succession ("resting cyst"), so as to enable it to resist prolonged desiccation, etc.: both differing from the hypnocyst in that their contents undergo brood formation. On encystment any indigestible food materials are extruded into the cyst, and in the "resting cysts," which are usually of at least two layers, this faecal mass lies in the space between them. The brood-cells escape, either as flagellate-cells, resembling the simpler Protomastigina, called "flagellulae," and which often become amoeboid (Fig. 29); or already furnished with pseudopodia, and called "amoebulae," though they usually recall Actinophrys rather than Amoeba. In Vampyrella and some others the amoebulae fuse, and so attain a greater size, which is most probably advantageous for feeding purposes. But usually it is as a uninucleate cell that the being encysts. They may feed either by ingestion by the pseudopodia, by the whole surface contained in a living host-cell, or by passing a pseudopodium into a host-cell (Fig. 29 5). They may be divided as follows:—

A. Myxoidea.—Flagella 1-3; zoospores separating at once.

1. Zoosporeae.—Brood-cells escaping as flagellulae, even if they become amoeboid later. Ciliophrys Cienk.; Pseudospora Cienk. (Fig. 29).

2. Azoosporeae.—Cells never flagellate. Protomyxa Haeckel; Plasmodiophora Woronin; Vampyrella Cienk.; Serumsporidium L. Pfeiffer.

B. Catallacta.—Brood-cells of cyst on liberation adhering at the centre to form a spherical colony, multiflagellate; afterwards separating, and becoming amoeboid. Magosphaera Haeckel (marine).[[95]]

Fig. 29.—Pseudospora lindstedtii. 1, 2, Flagellate zoospores; 3, young amoebula, with two contractile vacuoles, one being reconstituted by three minute formative vacuoles; 4, 5, an amoebula migrating to a fungus hypha through the wall of which it has sent a long pseudopodium; 6, amoebula full-grown; 7, 8, mature cells rounded off, protruding a flagellum, before encysting; 9, young sporocyst; 10, the nucleus has divided into a brood of eight; 11-14, stages of formation of zoospores. cv, Contractile vacuole; e, mass of faecal granules; fl, flagellum; n, nucleus, × about 750⁄1.

Plasmodiophora infests the roots of Crucifers, causing the disease known as "Hanburies," or "fingers and toes," in turnips, etc. Serumsporidium dwells in the body cavity of small Crustacea. Many of this group were described by Cienkowsky under the name of "Monadineae" (in Arch. Mikr. Anat. i. 1865, p. 203). Zopf has added more than anyone else since then to our knowledge. He monographed them under Cienkowsky's name, as a subordinate group of the Myxomycetes, "Pilzthiere oder Schleimpilze," in Schenk's Handb. d. Bot. vol. iii. pt. ii. (1887). To Lankester (Encycl. Brit., reprint 1891) we owe the name here adopted. Zopf has successfully pursued their study in recent papers in his Beitr. Nied. Org. The Chytridieae, usually ascribed to Fungi, are so closely allied to this group that Zopf proposes to include at least the Synchytrieae herein.