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54 ORGANIZATION OF THE INFUSORIA.structures and single-celled organisms, Professor Haeckel has recently proposedto introduce a special code of terminology. In connection with this heconfers upon all those cells, or so-called plastids, in which no nucleus ornucleus-like structure is present, the title of simple cytodes, reserving that oftrue cells for those alone in which such a structure is distinctly represented.Both of these are again recognized by this authority as including two minorgroups of equal value, distinguished by the presence or absence of abounding membrane or cell-wall ;the naked and membrane-boundedcytodes he has denominated respectively gymnocytodes and hullcytodes,and the nucleated cells in a similar manner, Urzellen or gymnocyta, andHullzellen or lepocyta. This separation of the nucleated and non-nucleatedunicellular structures generally, as applied to independent unicellular orProtozoic organisms in particular, forms the basis upon which ProfessorHaeckel has, as previously stated, proposed to establish his non-nucleatedclass-group of the Monera. In recognition of this same distinction, ProfessorHuxley, in his 'Anatomy of the Invertebrata,' has subdivided the Protozoainto the two groups of the Monera and Endoplastica ;the former correspondingwith the group of the same name as established by Haeckel,and the latter including that remaining great majority of the Protozoa inwhich an endoplastic or nucleus-like structure is distinctly visible. Sucha distinction is, nevertheless, adopted by this author as a matter only oftemporary convenience, he freely expressing his doubts as to whether itwill stand the test of extended investigation. The outcome of such researchsince the publicationof Professor Huxley's volume, has indeed fullyjustified the characteristic caution displayed by this eminent biologist ;several of the more important groups of the so-called Monera, includingmore especially the Foraminifera, being now found to consist of nucleatedstructures conforming in all essential details with that larger section of theProtozoa from which it has been proposed to separate them. In accordancewith the opinion maintained by the author of this volume, and as alreadyintimated in the preceding chapter, the Monera, as a distinct class, has nosubstantial claim for retention, all the representatives of the Protozoa beingheld to possess a nucleus, or its equivalent, in their fully matured condition.In their earliest and immature state this important structure, the nucleus,is undoubtedly, however, often absent, the Protozoon, under such conditionsonly, conforming in structure with Professor Haeckel's diagnosisof a simple cytode or Moneron. That a unicellular animal may, on theother hand, be entirely destitute of a differentiated bounding membrane, orcell-wall, is abundantly evident. All such peripheral differentiation isclearly conspicuous for its absence in the whole of that section of theProtozoa here distinguished by the title of the Pantostomata, and in whichfood-substances are incepted indifferently at any point of the periphery.As already indicated in the preceding chapter, this simplest and homogeneoustype of protoplasmic structure, the inseparable corollary of thePantostomatous organism,is found associated with by far the larger portion