CHAPTER XIII; 



SPECIAL MORPHOLOGY AND TAXONOMY OE THE 

 INFUSORIA. 



Since the first discovery of Vorticella and allied forms of Protozoa 

 by Leeuwenhoek in 1675, the Infusoria have been among the most 

 favored of living things studied through the microscope. The 

 designation Animalculae, given to include all forms of microscopic 

 life was changed by Ledenmiiller to Infusoria in 1760-1763, and the 

 entire phylum of Protozoa were included under this term by the 

 majority of writers down to Biitschli in 1882. Dujardin, 1841, 

 divided the "Infusoires" into rhizopods, flagellates and ciliates, a 

 classification adopted by Biitschli who, however, limited the use of 

 the term Infusoria to Protozoa bearing cilia at some period of the 

 life history. Two classes arc universally recognized today, the 

 Ciliata with permanent cilia, and Suctoria with cilia in the embry- 

 onic phases only. The classification of the Infusoria approaches 

 more closely to an ideal natural system than is possible at the 

 present time with any other group of Protozoa. 



In size the Infusoria vary from minute forms, 12 /j. in length 

 (some species of Cinetochilum, Aspidisca, etc.), to giant ciliates, up 

 to 3 mm. (Bursaria, Lionotus proceros (Fig. 44, p. 86), Spirostomum 

 ambiguum. Size, however, has little taxonomic value. 



The great majority of Infusoria are free-swimming but practically 

 all Suctoria and several minor groups of the Ciliata are attached, 

 while a few are parasitic. The majority of attached forms tend to 

 radial symmetry; free-swimming types show the greatest variety 

 of forms which in many cases may be traced to the effects of mode 

 of life, but the fantastic shapes of sapropelic and of many parasitic 

 types are difficult to reconcile with environmental conditions. The 

 ideal generalized form of Ciliata is a spherical or ellipsoidal organism 

 with the mouth at one end, contractile vacuole near the other, and 

 lines of cilia starting from the mouth and running in longitudinal 

 rows down the body. Shifting of the mouth with distortion of the 

 lines of cilia leads to various modifications of the generalized type 

 which is most closely represented by Holophrya or Prorodon species 

 (Fig. 191). A ventral surface bearing the mouth is established in the 

 Hypotrichida which includes some of the most highly specialized 

 forms of Protozoa. 



Tests, cups or "houses" are found here and there throughout the 

 entire group. Gelatinous secretions forming tubes (Stichotricha, 



