206 THE PROTOZOA 



this tube is not only retractile, but is also surrounded by four tentacle- 

 like processes which simulate some kinds of tentacles in the Suctoria. 

 As the majority of the larvae of the Suctoria are ciliated in girdles, 

 Haeckel holds that this division of the Holotrichida represents the 

 nearest allies of the Suctoria, and that the loss of cilia in the adult is 

 already foreshadowed by the regional loss of cilia in these girdled 

 forms. 



The entire matter, finally, of the origin of Infusoria from more 

 generalized forms of Protozoa remains unsolved ; the various 

 hypotheses are interesting possibilities, but no more can be said for 

 them. This problem, like that of the origin of the Protozoa, may 

 never come nearer settlement ; for, without the assistance of palaeonto- 

 logical and embryological evidence, which in other great groups of 

 the animal kingdom are of inestimable value in tracing ancestors, the 

 possibility of tracing their origin is reduced to a minimum. 



CLASSIFICATION 



CLASS V. INFUSORIA. Protozoa in which the motor apparatus is in the form of 

 cilia, either simple or united into membranes, membranelles, or cirri. The cilia 

 may be permanent or limited to the embryonic stages.' With two kinds of 

 nuclei, macronucleus and micronucleus. Reproduction is effected by simple 

 transverse division or by budding. Nutrition is holozoic or parasitic. 



Subclass I. CILIATA. Infusoria provided with cilia during adult as well as 

 embryonic life. Reproduction is brought about typically by simple transverse 

 division. Mouth and anus are usually present. The contractile vacuole is often 

 connected with a complicated canal system. 



Order i. HOLOTRICHIDA. Ciliata in which the cilia are similar and distributed all 

 over the body, with, however, a tendency to lengthen in the vicinity of the 

 mouth. Trichocysts are always present, either distributed about the body or 

 limited to a special region. 



Suborder I. GYMNOSTOMINA. Holotrichida without an undulating membrane 

 about the mouth, which remains closed except during food-taking intervals. t 



Family i. Enchelinidae. The mouth is always terminal or sub-terminal, and is 

 usually round or oval in outline. Food-taking is usually a process of swal- 

 lowing. Genera: Holophrya Ehr. ('31); Urotricha Clap. & Lach. ('58); 

 Enchelys Hill (1752), Ehr. ('38) ; Spathidium Duj. ('41) ; Chcenia Quennerstadt 

 ('68) ; Prorodon Ehr. ('33); Dinophrya Butschli ('88); Lacrymaria Ehr. ('30); 

 Trachelocerca Ehr. ('33); Actinobolus Stein ('67); Ileonema Stokes ('84); 

 Plagiopogon Stein ('59) ; Coleps Nitsch ('27) ; Tiarina Bergh ('79) ; Stepha- 

 nopogon Entz ('84) ; Didinium Stein ('59); Mesodinium Stein ('62); Butschlia 

 Schuberg ('86). 



Family 2. Trachelinidae. The body is distinctly bilateral or asymmetrical, with 

 one side, the dorsal, slightly arched. The mouth may be terminal or sub- 

 terminal, or the entire mouth-region may be drawn out into a long proboscis. 

 An oesophagus or gullet may or may not be present ; when present, it is usually 

 supported by a specialized framework. Genera: Amphileptus Ehr. ('30); 

 Lionotus Wrzesniowski ('70); Loxophyllum Duj. ('41); Trachelius Schrank 

 ('03) ; Dileptus Duj. ('41) ; Loxodes Ehr. ('30). 



