482 ORDER HOLOTRICHA. 



Order I. HOLOTRICHA, Stein. 



Animalcules free-swimming, more or less completely ciliate throughout ; 

 cilia alike or differing but slightly in character from one another, sometimes 

 supplemented by a variously modified extensile or undulating membrane ; 

 oral and anal orifices usually conspicuously developed ; the cuticular layer 

 or ectoplasm not unfrequently containing trichocysts. 



The order of the Holotricha was originated by Stein for the reception of all 

 those animalcules in which the surface of the integument is completely clothed with 

 cilia that agree entirely with or differ but slightly from one another in size and 

 character. It undoubtedly embodies the most simply organized members of the 

 class Ciliata, the series as a whole, however, being subject to considerable range 

 of complexity and offering a tolerably uniform series of gradations from the most 

 simple types towards the succeeding order of the Heterotricha. In those forms, 

 more especially such as Lembus, Pleuronema, Panophrys, and Cyclotricha, in which an 

 extensile or undulating adoral membrane is borne in addition to larger adoral cilia, 

 the highest differentiation and closest approximation to the Heterotrichous formula 

 is apparently arrived at It is noteworthy in connection with this circumstance 

 that the larger adoral fringe of cilia in both the Heterotrichous and Hypotri- 

 chous orders of the class, as typified by the two genera Stentor and Euplotes, is 

 represented in its earliest or initial state by a similar membraniform expansion. 

 Evidence indicative of the comparatively lower organization of the Holotrichous 

 group of the Ciliata, is afforded by their occasional sporular mode of reproduction. 

 This, while common to the Flagellata previously described, is as yet unknown among 

 the higher sections of the Ciliata. Illustrations of such exceptional developmental 

 phenomena are hereafter recorded in connection more especially with the four 

 genera Colpoda, Otostoma, Ichthyophthirius, and Amphileptus. 



In accordance with Stein's scheme of classification of the Ciliata,* reproduced at 

 page 210 of vol. i., the order of the Holotricha is, exclusive of the Opalinidae, sub- 

 divided into the four minor groups or families only of the Trachelina, Enchelina, 

 Paramsecina, and Cinetrochilina. It has been considered undesirable, however, to 

 adhere strictly to that scheme in this volume, and this in consequence not only of the 

 discoveries of numerous Holotrichous types requiring independent family grouping, 

 that have been made subsequent to the appearance of Stein's work, but on account 

 also of the evident incongruity in many instances of the generic groups united 

 under his proposed family headings. Examining these five family groups in 

 successive order, it will be found that the title of the last one, that of the 

 Cinetrochilina, has to be entirely abandoned, since Cinetrochilum and its supposed 

 near ally Glaucoma can no longer be accepted as independent generic types but 

 as being developmental conditions only of certain Hypotricha. Pleuronema 

 and Cyclidium, again, differ so remarkably in the character of their membrani- 

 form appendages from Lembadion, Ophryoglena, and the several other generic 

 types with which Stein associates them, as to demand independent family dis- 

 tinction. In Stein's fourth family of the Paramaecina a still more heterogeneous 

 assemblage of generic forms is encountered, the proposed group including, in addition 

 to the simply and evenly ciliate Paramada, the diversely ciliated Enchelys, Nassula 

 with its fish-trap-like pharyngeal armature, the membranous flap-bearing Panophrys, 

 and various other distinct types. His third family of the Enchelina is composed 

 of equally inconsistent elements as typified by such entirely dissimilar generic types 

 as Prorodon which is immediately allied to Nassula Coleps, Lacrymaria, Perisfira, 

 and Actinobolus. The last-named generic form would seem indeed to have no 



* 'Infusionsthiere,' Abth. ii., 1867. 



