INFUSORIA. 31 



the true infusorial forms into two orders, — Astoma, without oral aperture and Stoma- 

 toda, with a distinct oral aperture and cesophagus. Claparede and Lachmann, in 1868, 

 for the first time restricted the group to its present limits, and divided it into four orders, 

 I. Flagellata, II. Cilio-flagellata, III. Suctoria, IV. Ciliata. Stein in his magnificent 

 work, "Organismus der Infusionsthiere," not yet completed, presented in 1867 the 

 classification of the Ciliata now generally adopted. The part of the work treating of 

 the Flagellata appeared in 1878 ; it includes several genera, by many regarded as 

 undoubted plants — for example, Volvox and Chlamydomonas. The latest proposed 

 arrangement, by W. Saville Kent, in his Manual of the Infusoria (1880-82), divides 

 the Legion Infusoria into the following classes : I. Flagellata, II. Ciliata, III. Tenta- 

 culifera. This author's limitation and arrangement of this group will be adhered to 

 in the following pages, except tliat the Infusoria will be regarded as a Class ; hence, 

 his classes will become Orders and his Orders sub-orders. 



Order I. — FLAGELLATA. 



The Infusoria of this order bear one, two, or more flagella, which serve them for 

 locomotion, and assist in obtaining food. They were not unknown to the earliest 

 observers. In 1696, Mr. John Harris described what is undoubtedly Euglena viridis ; 

 but the modern microscope alone can reveal their oi-ganization, and it is in the study of 

 these lowly organisnas that the most substantial progress has been made by recent in- 

 vestigators in this field of research. Reference may here be made to the discovery of 

 the collared-monads by H. J. Clark in 1868, and the addition of numerous species to 

 this list by Stein and Kent, and also to the fact that Stein has foimd many Flagellata 

 more highly organized than had been previously supposed. He has shown that many of 

 the Flagellata possess well developed oral apertures, frequently with the addition of a 

 pharyngeal dilation, and occasionally a buccal armature similar to that of the Ciliata. 

 The flagellum is not the only means of locomotion possessed by some species, like 

 Mastigamceba, for these have true pseudopodia like those of Amoeba ; others, again, as 

 Actinomo7ias, have, besides the flagellum, temporarily developed rays like Actino- 

 phrys ; a thread-like pedicle is also present in Actinomonas. 



Sub-Oeder I. — Teypanosomata. 



The very lowest of the Flagellata now known are two parasitic forms, one of 

 which {Tryjxmosoma sanyuinis) is illustrated by 

 Fig. 24. The animal is flattened, and has a frill- 

 like, undulating, lateral border which serves for loco- 

 motion. It will be seen that one extremity is somewhat 

 prolonged or attenuate, representing the flagellum ; 

 the species occurs in the blood of frogs; its congener ^"*" "*\raguitoi"cS'tiiues."''"""*' 

 inhabits the intestine of domestic poultry. 



Sub-Order II. — Rhizo-flagellata. 



There occur in pond water, hay-infusions, and the like, some most interesting forms ; 

 they are so because they have characters in common with the Amoeba; that is, they 



