CILIATA 



53 



of cilia, which are stout and resemble fine -pointed cirrhi. 

 In Dysteria the cilia are exclusively ventral, and the naked 

 dorsal surface has its pellicle condensed into a bivalve shell ; a 

 posterior motile process (" foot ") and a complex pharyngeal 

 armature add to the exceptional characters of the genus. 



The Aspirotrichaceae are well known to every student of 

 "Elementary Biology" by the "type" Paramecium (Fig. 55), 

 so common in infusions, especially when containing a little 

 animal matter. P. bursaria often contains in its endosarc the 



Fig. 56. Tracheitis ovum. A, general view ; B, section through sucker ; C, section 

 through contractile vacuole and its pore of discharge, al, Alveolar layer of ecto- 

 plasm ; cil, cilia ; c.v, contractile vacuole ; m, mouth ; A, meganucleus ; s, sucker, 

 from which pass inwards retractile myonemes. (After Clara Hamburger. ) 



green symbiotic Flagellate Zoochlorella. Colpoda cucullus, very 

 frequent in vegetable infusions, usually only divides during 

 encystment, and forms a brood of four. Pleuronema chrysalis 

 (Fig. 57) is remarkable for its habit of lying for long periods 

 on its side and for its immense undulating membrane, forming 

 a lip on the left of its mouth ; Glaucoma has two, right and left. 

 The Heterotrichaceae present very remarkable forms. Spiro- 

 stomum is nearly cylindrical, and, a very giant, may attain a 



extension of the front of the body above and beyond the mouth ; all three swim with 

 peculiar grace. Trachelitis (Fig. 56) has a distinct cup-shaped sucker behind the 

 mouth, and is remarkable, like Loxodes, for the branching disposition of its 

 endosarc. 



