44 THE SUB-KINGDOM PROTOZOA. 



association with the Amoebina as is presented by the Opalinida with 

 relation to the normal Ciliata. All pass an endoparasitic condition within 

 the viscera of other animals, and derive their sustenance through the direct 

 imbibition or endosmosis of the juices of the selected host through their 

 cuticular surface. 



While the foregoing sketch suffices to indicate the leading aspects and 

 characteristics of the Protozoic sub-kingdom generally, and to explain the 

 view of the derivation and affinities of the various orders adopted by the 

 author of this volume, a few other points demand brief attention. Among 

 these, reference has yet to be made to the undoubtedly close relationship 

 which subsists between the lowest members of the Protozoic sub-kingdom 

 and the unicellular members of the vegetable world, and to the opinions 

 maintained in this direction by recent authorities of note. The difficulty of 

 indicating a clear line of demarcation that shall arbitrarily separate certain 

 unicellular cryptogamic plants or Protophyta from the unicellular animals or 

 Protozoa, has long been recognized, and even at the present day cannot be 

 said to have obtained its final solution. It is, indeed, scarcely to be antici- 

 pated that any such result should be arrived at, since here, as between many 

 other arbitrarily defined so-called natural classes and subdivisions of the 

 animal and vegetable worlds, modern discovery is unceasingly revealing 

 the existence of intermediate forms that, filling up the pre-existing lacunae, 

 further demonstrate the harmonious continuity of the entire organic series. 

 Taxonomy, or classification, through this consideration, is necessarily reduced 

 to a purely empirical and constantly progressive status, to an artificial 

 means for the demarcation of those boundaries or landmarks most clearly 

 conspicuous to our appreciation, that system recommending itself most, 

 and having the most lasting duration, whose foundations are established 

 upon the most simple and natural basis. 



Failing to eliminate such a natural or artificial boundary line as shall 

 serve to decisively mark out the apparently intersecting zones of animal 

 and vegetable life, one of the foremost biologists of the age, Professor 

 Ernst Haeckel, has elected to establish yet a third kingdom of the organic 

 world, to which he has relegated not only all dubious types, but also 

 many concerning whose animal or vegetable nature not so much as a doubt 

 exists. This proposed new organic kingdom, denominated by its founder 

 the " Protista," is, with the exception of the Ciliata, Spongida, and Ten- 

 taculifera, made to include all the members of the Protozoa embraced m 

 the previously submitted scheme, and in addition to these, the assemblage 

 of undoubted vegetable organisms forming the tribe of the Diatomaceae. 

 This attempt to cut the Gordian knot by the interpellation of a third 

 and intermediate kingdom, is by no means happy. Even if this latter 

 possessed in itself the elements of stability, the difficulty would be in no 

 ways lessened, but simply augmented, as there \vould be now two lines 

 of demarcation, one between the Protista and vegetable forms, and the 

 other between the Protista and the animal series, to be defined in place 



