42 THE SUB-KINGDOM PROTOZOA. 



or nucleus, being thus in no way distinguishable from the typical repre- 

 sentatives of the ordinary Flagellata-Pantostomata, as met with in the 

 genus Monas. By-and-by these monadiform zooids become more sluggish, 

 subside to the bottom of the inhabited fluid medium, and for a while 

 retaining their flagella, creep about after the manner of a Mastigam&ba, 

 incepting in the same way solid food-particles at any point of the periphery. 

 The zooids in this condition may be said to represent the adult form 

 of the Rhizo-Flagellata. Sooner or later the flagella are withdrawn, and 

 an entirely amoeboid condition is assumed. These amoeboid zooids, 

 encountering their fellows in the course of their wanderings, at once co- 

 alesce with them, and form at length by their amalgamated numbers and 

 increase of size through the incessant increment of food, those conspicuously 

 large masses of gelatinous consistence, characteristic of the so-called animal 

 phase of the Myxomycetan, technically known as the " plasmodium." 

 This plasmodium, exhibiting diverse forms in various species, may be 

 found creeping over wet tan, rotten wood, or decaying leaves in the 

 similitude of a colossal Amceba, or, taking a reticulate form, spreads 

 itself over the surface of these substances, and presents under such con- 

 ditions the aspect of the mycelia of various fungi. Examined with the 

 microscope, all trace of the multicellular or multizooidal origin of the 

 plasmodium is found to have disappeared, the entire mass exhibiting the 

 character of homogeneous granular sarcode. A greater or less number 

 of rhythmically pulsating contractile vesicles are discernible at various 

 points, and a distinct circulatory motion or cyclosis of the granular 

 plasma, sometimes in a single and sometimes in contrary directions, 

 is exhibited within the deeper substance of the plasmodium. This 

 phenomenon of cyclosis is most readily observed in those forms, like 

 Didymium serpula, in which the plasmodium assumes a reticulate or 

 much ramified mycelium-like outline, the motile currents of sarcode 

 under such conditions closely corresponding with those common to the 

 pseudopodic reticulations and ramifications of the Foraminifera and 

 Labyrinthulina. Following upon the plasmodium state, the highly charac- 

 teristic so-called vegetable phase is now arrived at. In this condition 

 animal vitality is apparently entirely suspended, the aspect being usually 

 that of a minute Gasteromycetous fungus, mostly stalked, and with a 

 spheroidal, ovate, or urn-shaped capitulum or sporangium. The outer wall 

 of this capitulum is more or less coriaceous, and is found interiorly to be 

 densely packed with spore-like bodies, mostly held together by a dense 

 network of delicate anastomosing fibres of a horn-like consistence. By 

 the dehiscence of a cup-like lid or the disintegration of the walls of the 

 sporangium, the contained spores are eventually liberated and repeat the 

 metamorphoses just described. It is upon the external likeness to certain 

 fungi of the quiescent sporangia of the Myxomycetes, as developed from 

 the plasmodium, that the arguments in favour of the vegetable nature 

 of these singular organisms have been chiefly based. 



