556 ORDER HOLOTRICHA. 



Hab. — Intestinal tract of American white ant, Teruies flavipes (Jos. 

 Leidy). 



This type is described by Professor Leidy as being the most minute and at the 

 same time the most abundant of the three forms with which Tcrmes flavipes was 

 found endoparasiticaUy infested. Its movements correspond ahiiost precisely with 

 those of Trichonympha and Pyrsonympha, being hmited mostly to active writhing 

 motions and to a lengthening and contraction of the body, accompanied by occasional 

 rotation on its long axis ; the animalcule otherwise maintains a nearly stationary 

 position. It has been recently suggested by its discoverer as by no means improbable 

 that Di)ienympha may eventually prove to be a younger condition of Pyrsonympha. 

 If, however, his interpretation of the internal development of sporular elements, as 

 represented at PI. XXVIII. Fig. 21, is correct, its claim for independent recognition 

 would appear to be fully substantiated. 



Appendix A. HOLOTRICHA-ASTOMATA. 



Animalcules free-swimming, more or less completely and evenly ciliate 

 throughout ; possessing no oral aperture. 



Fam. XIII. OPALINIDiE, Stein. 



Animalcules free-swimming or temporarily adherent, mouthless, finely 

 and equally ciliate throughout, the cilia usually presenting a tufted or 

 matted aspect ; the anterior extremity sometimes armed with differentiated 

 organs of prehension, which may take the form of a suctorial disc, or 

 of one or more horny bands or uncini ; endoplast conspicuously developed, 

 sometimes multiple ; contractile vesicle present or absent. Occurring as 

 endoparasites within the recta and intestinal viscera of Amphibia and 

 Invertebrata. 



The representatives of this family group were originally separated by Siebold 

 from the ranks of the ordinary Ciliate Infusoria and placed together with the 

 Peridiniidce, Euglenidae, and other Flagellate Protozoa — then supposed to be mouth- 

 less — in a separate section denominated by him the Astomata. All these flagellate 

 forms are now, however, with but few exceptions, known to possess either a distinct 

 oral aperture or the faculty of ingesting solid food-substances through a more or less 

 widely distributed area of their periphery ; while, in accordance with the views of 

 Stein and other recent authorities, the Opalinidc^ are to be regarded rather as an 

 aberrant and retrograde group of the ordinary Holotrichous series than as an entirely 

 distinct order of the Ciliata. Accepted upon such terms, the mouthless condition of 

 these aberrant Infusoria may be consistently interpreted as representing the outcome 

 of long subjection to that endoparasitic mode of existence which, among the normal 

 Rhizopoda, Annelida, and Crustacea, has apparently in an equivalent manner produced 

 the correspondingly mouthless groups of the Gregarinida, Cestoidea, and Rhizocephala. 

 The isomorphic, or more correctly the homoplastic, external resemblance that sub- 

 sists between many Opalinidse and certain Cestoid worms or Entozoa, is truly 

 remarkable, lending considerable weight to the opinion maintained by many earlier 

 writers that these animalcules are not independent beings, but embryonic or larval 

 conditions only of these higher Metazoa. The superficial resemblance cited is more 

 especially manifested in connection with the structural modifications exhibited by 

 the two genera Haptophrya and Boplitophrya, in which, respectively, adhesive aceta- 

 bula or corneous booklets, similar to those of many higher Entozoa, are developed 



