54 ORGANIZATION OF THE INFUSORIA. 



structures and single-celled organisms, Professor Haeckel has recently pro- 

 posed to introduce a special code of terminology. In connection with this he 

 confers upon all those cells, or so-called plastids, in which no nucleus or 

 nucleus-like structure is present, the title of simple cytodes, reserving that of 

 true cells for those alone in which such a structure is distinctly represented. 

 Both of these are again recognized by this authority as including two minor 

 groups of equal value, distinguished by the presence or absence of a 

 bounding membrane or cell-wall ; the naked and membrane-bounded 

 cytodes he has denominated respectively gymnocytodes and hullcytodes, 

 and the nucleated cells in a similar manner, Urzellen or gymnocyta, and 

 Hullzellen or lepocyta. This separation of the nucleated and non-nucleated 

 unicellular structures generally, as applied to independent unicellular or 

 Protozoic organisms in particular, forms the basis upon which Professor 

 Haeckel has, as previously stated, proposed to establish his non-nucleated 

 class-group of the Monera. In recognition of this same distinction, Professor 

 Huxley, in his 'Anatomy of the Invertebrata,' has subdivided the Protozoa 

 into the two groups of the Monera and Endoplastica ; the former corre- 

 sponding with the group of the same name as established by Haeckel, 

 and the latter including that remaining great majority of the Protozoa in 

 which an endoplastic or nucleus-like structure is distinctly visible. Such 

 a distinction is, nevertheless, adopted by this author as a matter only of 

 temporary convenience, he freely expressing his doubts as to whether it 

 will stand the test of extended investigation. The outcome of such research 

 since the publication of Professor Huxley's volume, has indeed fully 

 justified the characteristic caution displayed by this eminent biologist ; 

 several of the more important groups of the so-called Monera, including 

 more especially the Foraminifera, being now found to consist of nucleated 

 structures conforming in all essential details with that larger section of the 

 Protozoa from which it has been proposed to separate them. In accordance 

 with the opinion maintained by the author of this volume, and as already 

 intimated in the preceding chapter, the Monera, as a distinct class, has no 

 substantial claim for retention, all the representatives of the Protozoa being 

 held 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 condi- 

 tions only, conforming in structure with Professor Haeckel's diagnosis 

 of a simple cytode or Moneron. That a unicellular animal may, on the 

 other hand, be entirely destitute of a differentiated bounding membrane, or 

 cell-wall, is abundantly evident. All such peripheral differentiation is 

 clearly conspicuous for its absence in the whole of that section of the 

 Protozoa here distinguished by the title of the Pantostomata, and in which 

 food-substances are incepted indifferently at any point of the periphery. 

 As already indicated in the preceding chapter, this simplest and homo- 

 geneous type of protoplasmic structure, the inseparable corollary of the 

 Pantostomatous organism, is found associated with by far the larger portion 



