_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 {90}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. This group is very closely allied to Sporozoa; for the absence of cytogamy, and of sickle-germs,[96] and of the complex spores and cysts of the Neosporidia, are the only absolute distinctions. 6. MYCETOZOA (MYXOMYCETES, MYXOGASTRES) _Sarcodina moving and feeding by pseudopodia, with no skeleton, aggregating more or less completely into complex "fructifications" before forming 1-nucleate resting spores; these may in the first instance liberate flagellate zoospores, which afterwards become amoeboid, or may be amoeboid from the first; zoospores capable of forming hypnocysts from which the contents escape in the original form._ 1. Aggregation taking place without plastogamy, zoospores amoeboid, with a clear ectosarc ACRASIEAE. _Copromyxa_ Zopf; _Dictyostelium_ Brefeld. 2. Aggregation remaining lax, with merely thread-like connexions, except when encystment is to take place; cytoplasm finely granular throughout; complete fusion of the cytoplasm doubtful FILOPLASMODIEAE. _Labyrinthula_ Cienk.; _Chlamydomyxa_ Archer; _Leydenia_ (?) Schaud. 3. Plasmodium formation complete, eventuating in the formation of a complex fructification often traversed by elastic, hygroscopic threads, which by their contraction scatter the spores; zoospores usually flagellate at first MYXOMYCETES. _Fuligo_ Hall.; _Chondrioderma_ Rostaf.; _Didymium_ Schrad. (Fig. 30). I. The ACRASIEAE are a small group of saprophytes, often in the most literal sense, though in some cases it has been proved that the actual food is the bacteria of putrefaction. In them, since no cell-division takes place in the fructification, it is certain that the multiplication of the species must be due to the fissions of the amoeboid zoospores, which often have the habit of _Amoeba limax_ (Fig. 1, p. 5).