IS4 



PROTOZOA 



length of 4 mm. (^"). Stentor can attach itself by its hinder end, 

 which is then finely tapered and prolonged into a few pseudopodia ; 

 its body is trumpet-shaped, with a spiral peristome forming a 

 coil round its wide end, and leading on the left side into the 

 mouth. Many species when attached secrete a gelatinous sheath 

 or tube. *S^. polymorphus is often coloured green by Zoochlorella 

 (p. 125); S. coeruleus^ and S. igneus owe their names to the 

 brilliant pigment, blue or scarlet, deposited in granules in lines 

 between the conspicuous longitudinal myonemes. From their 



Fio. 57. — Pleuronema chrysalis (Aspirotrichaceae). A, Unstimulated, lying quiet ; 

 B, stimulated, in the act of springing by the strolie of its cilia. (From Verworn.) 



large size and elongated meganucleus accompanied by numerous 

 micronuclei, these two genera have frequently been utilised for 

 experiments on regeneration. In Metopus sigmoides the peri- 

 stomial area forms a dome above its wreath of membranellae ; 

 and in M. pyriformis this is so great as to form the larger part 

 of the cell, which is top -shaped, tapering behind to a point. 

 Caenomorpha (Fig. 58) has the same general form, with a peg- 

 like tail, and possesses a girdle of cirrhi.^ The converse occurs in 



' The pigment of this species has been examined and described by Lankestor 

 under the name of "blue stentorin" {Quart. Joicrn. Mier. Sci. xii. 1873). 



2 For a full account of Caenomorpha, Metopus, and allied forms, see Levander, 

 Beitr. z. Kenntn. einiger Ciliaien, Dissert. Helsingfors, 1894. 



