THE INFUSORIA 



399 



times reach a total length of 3 mm. Marine. Prorodon, Ehrb. 

 Usually spherical in form, with a well -developed pharyngeal armature. 

 1 mm. Freshwater. (Fig. 8.) Perispi-ra, Stein. Bands of cilia arranged 

 in a spiral manner. 0'05. Stagnant freshwater. Chaenia, Quenn. An 

 elongated and contractile form with a special group of long cilia at the 

 anterior attenuated extremity. 0*25. Marine. 



Family ACTINOBOLINA, Stein. Actinobolus, Stein (Fig. 48). Spherical 

 in shape, provided with a uniform covering of long cilia. The most 

 remarkable feature of this genus is the power they possess of protruding 

 a considerable number of long, needle-shaped protoplasmic processes or 

 tentacles, each armed at its extremity with a large trichocyst. O'l. 





Fid. 48 



Actinobolus radians, Stein, with the peculiar tentacles (t, t) 

 fully extended. Each tentacle bears at its extremity a tricho- 

 cyst. ra, mouth ; M, meganucleus ; c.v, contractile vacuole ; 

 c, c, cluster of cilia at the insertion of the tentacles. (After 

 Schewiakoff.) x 400. 



FIG. 49. 



lleonema dispar, Stokes. 

 M, meganucleus ; o, 

 mouth ; a.p, anterior 

 prehensile appendage ; 

 c.v, contractile vacuole. 

 (After Schewiakoff.) 

 x 300. 



Freshwater. lleonema, Stokes". Flask -shaped, with a long prehensile 

 appendage springing from the oral extremity (Fig. 49). 0'2. Freshwater. 



Family COLEPINA, Ehrb. Plagiopogon, Stein. Without carapace. 

 Very small. Freshwater. Coleps, Nitzsch. Body covered by a compli- 

 cated carapace (Fig. 5). 0'05. Freshwater. Tiarina, Bergh. Similar to 

 the above, but with a pointed posterior extremity. Marine. Stephanopogon, 

 Entz. Slightly elongated forms, flattened on ventral side, with a large 

 horse-shoe meganucleus. 0'07. Marine. 



Family CYCLODININA, Stein. Dinophrya, Biitschli. Cylindrical in 

 form, with a pointed posterior extremity. 0*1. Freshwater. Didinium, 

 Stein (Fig. 74). Cylindrical in form, with a conical peristome. Cilia 

 restricted to a few circular . bands. Mouth capable of extraordinary 

 dilatation. 0-2. Freshwater. Mesodinium, Stein. Cilia reduced to a 

 single band, very long and strong. 0*04. Marine and freshwater. 



