This name has been proposed by Haeckel for certain singular organisms which may provisionally be regarded as the lowest group of the Rhizopoda. They are very minute in size, and are distinguished by the fact that the body is composed of structureless sarcode, capable of emitting thread-like prolongations or pseudopodia, but destitute of either nucleus or contractile vesicle. The pseudopodia are mostly in the form of delicate filamentous processes of sarcode, which exhibit a circulation of minute molecules and granules in their interior and along their edges. Sometimes the pseudopodia may be simple, as in Protamoeba (fig. 7, a), or they may be ramified and anastomosing, as in Protogenes. The form of the body, though very mutable, may be simple; or the organism may form a kind of colony of protoplasmic masses united by their interlacing pseudopodia (as in Myxodictyon). Sometimes the organism passes through a quiescent stage, alternating with an active and locomotive phase of existence. No hard covering or "test" is ever developed. Reproduction is mostly by fission, with or without precedent encystation (fig. 7, b and c) and quiescence. All the Monera live in water, and their systematic position is uncertain. From the general nature of the pseudopodia, and the fact that the sarcode is not differentiated into an "ectosarc" and an "en-dosarc," they appear to be most nearly allied upon the whole to the Foraminifera, from which they differ chiefly in the absence of a shell defending the soft protoplasm of the body, as well as in the constant absence of a nucleus.
Fig. 7. - Morphology of Monera. a Protamoeba porrecta; b Protomyxa auran-tiaca ; c The same in an encysted condition. Greatly magnified.
The name of Bathybius was given by Professor Huxley to a structure believed to consist of irregular, formless, diffused masses of protoplasm, without nucleus or contractile vesicle, found at great depths in the sea; and, if organic, the place of Bathybius would be amongst the Monera. More recently, however, Professor Huxley and Sir Wyville Thomson have expressed the opinion that Bathybius is not really a living organism at all; and it only requires mention here because a similar structure, the true nature of which still requires investigation, has recently been described by Bessels under the name of Protobathybius.