106 ORGANIZATION OF THE INFUSORIA. 



In certain important points, nevertheless, it will be found that another 

 sub-order, that of the Hypotricha, commends itself equally as a candidate for 

 recognition. It is, for instance, undoubtedly among the representatives of 

 the genera Stylonychia, Euplotes, and other Oxytrichidae that we find the 

 most elaborate differentiations of the Ciliate type, certain of the numerous 

 and diversely modified groups of appendages being severally set apart for 

 the accomplishment of the special functions of food-collection, natation, and 

 even ambulation. Such forms, although not indicating any homoplastic 

 affinity, as in the previously cited cases, with the Metazoic series, un- 

 doubtedly represent the as yet known most highly specialized type of a 

 simple unicellular animal or Protozoon, and exhibit in this respect, as 

 compared to the other sections of the Ciliata, a type of organization 

 parallel to that which obtains among the higher Insecta with relation to 

 the Annelidous or Myriapodous groups of the Arthropoda. It is not, 

 however, in either of these more highly specialized divisions that the phylum 

 of evolution onwards and towards the yet higher groups of the organic 

 world is to be sought. Such differentiated types represent merely the 

 most advanced and terminal series of an entirely divergent and independent 

 branch or outgrowth from the parent stock. In yet another point, the 

 Hypotrichous sub-order of the Ciliata would seem to lay claim to a higher 

 grade of organization than that possessed by the Peritricha. In their 

 phenomena of reproduction the processes of conjugation, as exhibited by 

 these two sections, are conspicuously distinct, being in the case of the 

 Peritricha complete and permanent, as with the Flagellata and lower 

 Protophytes, while with the Oxytrichidae, and also certain Holotricha, such 

 as Paramecium, the conjugative act is only transitory, the two conjugated 

 individuals finally separating and renewing their independent existence. 

 The approximation in the latter instance towards the genetic reproductive 

 process of the Metazoic series, and in the former case towards the simpler 

 vegetative one known as " zygosis," as it occurs among the lower plants, 

 is self-suggestive, and affords an additional element for consideration in 

 summing up the evidence in favour of the higher organization of these 

 respective groups. 



The apparent affinities of the Tentaculiferous class of the Infusoria 

 with reference to the Metazoic series has been already discussed, but not so 

 those that obtain between the Tentaculifera and the Ciliate division of the 

 same group. Excepting for the data yielded by the phenomena of develop- 

 ment, no direct relationship indeed would seem to subsist between the two, 

 neither cilia, flagella, nor any recognizable modifications of those appendages 

 being characteristic of the adult forms. In place of such organs these 

 animalcules possess suctorial or prehensile tentacula, which, as explained 

 at length on a previous page, more closely approach, in their simplest 

 condition, the extensile ray-like pseudopodia of Actinophrys and other 

 Radiolaria. The free-swimming larvae or embryos of all Tentaculifera 

 are, nevertheless, characterized by the possession of a more or less com- 



