DERIVED ORGANIZATION— TAXONOMIC STRUCTURES U\i 



strength of these cytostomial supports seem to be entirely out of 

 proportion to such hypothetical needs of the organism. Thus in 

 all of the Chlamydodontidae the trichites form a tubular armature, 

 the ends making a circumoral ring which may project beyond the 

 ventral surface (Chilodon cucullus). Such an aggregate, known as 

 an oral or pharyngeal basket, or pharyngeal armature, forms a more 

 or less definite cytopharynx. In some cases the trichites are re- 

 placed by a compact corneus tube which extends dee]) into the 

 endoplasm as in Nassula aurea, Orthodon hamatus, Trachelitis ovum, 

 etc. (Fig. 93). 





mm >' 





A 



B 



C 



Fig. 93.-^4., Orthodon hamatus with oral tube; B, Frontonia leucas. with undulating 

 membrane on left margin of mouth; C, Trachelitis ovum. (A and C, after Biitschli; B, 

 after Calkins.) 



In the Trichostomina the permanently open mouth always leads 

 into a more or less highly-developed gullet or cytopharynx, while 

 peristomial cortical differentiations of various kinds lead to it. 

 The cytopharynx is usually provided with one or more undulating 

 membranes, while membranelles, undulating membranes and cirri 

 may also be present in the peristome. These are well illustrated 

 bv the complex oral apparatus of Glaucoma {Dallasia) frontata 

 (Fig. 8, p. 29). 



The mouth region of the ciliates appears to be the focal point of 

 the longitudinal rows of cilia. In the generalized forms, such as 

 Actinobolina radians, Prorodon teres, Holophrya discolor, etc., the 

 mouth is exactly terminal and the rows of cilia run symmetrically 



