MORPHOLOGY AND TAXONOMY OF THE INFUSORIA 483 



they are replaced in part or entirely by cirri. Here, also, particu- 

 larly in parasitic forms (Ophryoscolecidae and Cycloposthiidae), the 

 periplast is well developed and the organisms are frequently char- 

 acterized by fantastic sculpturing (Fig. 146, p. 293). 



The sub-class Chonotricha includes a small number of forms 

 with highly exaggerated peristomial structures. These are spirally 

 wound (to the right) in Spirochonidae but are funnel-shape in 

 Chilodochonidae. The characteristic reproduction by budding in 

 these forms suggests a relationship to the Suctoria. 



Parasitism in Infusoria, as in other great groups of Protozoa, is 

 widely spread and some of the adaptations to this end merit special 

 consideration. The majority are apparently harmless commensals 

 of digestive tract and body cavity; some, however, are more serious, 

 Balantidium coll for example, causing acute enteritis in man and 

 other mammals. Ectoparasitic forms may also be a source of 

 trouble. Amphileptus branchiarum gets under the gill mantles of 

 tadpoles and ingests groups of epithelial cells (Wenrich) ; others form 

 peculiar arms by which they are anchored to gill bars (Ellobiophrya 

 donacis Chatton, Fig. 104, p. 202). In the main, related forms are not 

 strictly parasitic but are attached in gill chambers where a constant 

 supply of food is assured. Special attaching organs, arising from 

 specially modified cilia, are characteristic of holotrichous and of 

 some peritrichous forms. These are best developed in Trichodina 

 (common on Hydra) where a special attaching organ termed the 

 scopula is characteristic, while the two arms of Ellobiophrya men- 

 tioned above are interpreted by Chatton as representing a split 

 scopula. Amongst the Holotrichida, ectoparasitism is character- 

 istic of the group which Chatton calls the Thigmotricha (1923). 

 Here a portion of the posterior ciliated region termed the " thigmo- 

 tactic area" becomes modified as an attaching organ. It is a sucking 

 disc in Ptychostomum, a protrusible tentacle in Hypocomidcs and 

 Hypocoma which Chatton, correctly, removes from the Suctoria to 

 the Holotrichida. It is rudimentary in Plagiospira and not at all 

 evident in Boveria. Two types of feeding adaptations are evident 

 in these forms. In one series the peristome and adoral zone become 

 greatly enlarged, forming a helicoid spiral in Boveria, Plagiospira, 

 Hemispira and Ancistruma, capable of drawing in food particles 

 from a distance. In another series the oral apparatus becomes 

 rudimentary or lost altogether, food substances being absorbed by 

 osmosis through the general body wall or by tentacles only as in 

 Hypocoma and Hypocomides. 



Lumen-dwelling forms have apparently undergone less degenera- 

 tion than have ectoparasitic types. In the Astomida such degen- 

 eration has been the most extreme. Here mouth and other oral 

 structures are entirely wanting and nutrition is osmotic. In the 

 majority of cases, however, the peristome and mouth are retained 



