MORPHOLOGY AND TAXONOMY OF THE INFUSORIA 481 



victim and digests its endoplasm in situ (Maupas, 1883). Ten- 

 tacles for adhesion are also present in Mesodinium (Fig. 198). 



While the vast majority of Infusoria are holozoic in food -get ting, 

 parasitic types may be holozoic or saprozoic (Astomida). Proteins 

 are digested by all and carbohydrates in some (Balantidium Glaess- 

 ner, see p. 198). 



Adaptations for food-getting, protection during ingestion and 

 other differentiations in the service of nutrition are responsible for 

 most of the cortical structures of the derived organization and 

 these for the most part determine the taxonomic position of genera. 

 Trichocysts, trichites, pharyngeal baskets, etc., have been described 

 (see p. 478). Adhesive discs (Lichnophoridae, Urceolariidae) ; thig- 

 motactic cilia or special cilia for attachment ("Thigmotricha" of 

 Chatton, Boveriidae, Aucistrumidae, Conchophthiriidae) and 

 suckers for attachment (some Astomida, Mesodinium, etc.) or for 

 food-getting (Hypocomidae, Suctoria) are widely distributed. The 

 most important, taxonomically, of all of these adaptations are those 

 associated with the filiate mouth. In the classification adopted 

 here we follow the recent trend (Poche, Kahl, Reichenow-Dorlein, 

 et id.) in filiate morphology in which the oral apparatus together 

 with position on the body are primary diagnostic characters. The 

 absence of an adoral zone of membranelles about the mouth (peri- 

 stome) distinguishes the' sub-class Holotricha from other ciliates. 

 The direction of curvature of the adoral zone, and spiral rows of 

 cilia in the sub-class Chonotricha distinguishes the sub-class Peri- 

 tricha. Here, however, sonic confusion results from use of the 

 terms left -wound and right-wound. Obviously a left-wound spiral 

 becomes a right-wound spiral if the start is made from the end 

 away from the mouth. Stein, Biitschli and others, until quite 

 recently, viewed the spiral as starting from the mouth and inter- 

 preted the adoral zones of Peritromus, Stentor, Stylonyehia, et <d., 

 as wound to the left, whereas in the Peritricha it winds to the right. 

 Kahl, Reichenow-Doflein and other recent writers view the spiral 

 as starting from the end farthest away from the mouth with a 

 corresponding reversal in use of the descriptive terms left and 

 right. Since the stroke of the membranelles and the food currents 

 are toward the mouth, the modern point of view probably has more 

 justification than the older one and is adopted here. It makes a 

 difference furthermore whether the organism is viewed from the 

 ventral or dorsal aspect; for right and left as used above the organism 

 is viewed from the oral side. 



The mouth proper may be provided with simple cilia or com- 

 binations of cilia, or void of cilia altogether. Those without motile 

 elements are grouped in the order Gymnostomida established by 

 Biitschli. These in turn are distributed in sub-orders according 

 to the position of the mouth. In the sub-order Prostomina the 

 31 



