26 



THE BIOLOGY OF ST EN TOR 



7. Cystment 



Hibernation in a cyst may be regarded as a response of Stentor 

 to adverse conditions. Stein's is the only published account and 

 characteristically he provided beautiful illustration of coeruleus 

 and polymorphus cysts (1867, Tafeln V and VI). Although the 

 final test of excystment was lacking, he can hardly have been 

 mistaken because the coeruleus capsules retained the blue-green 

 striping and the polymorphus were of similar form, with chlorellae 

 and colorless stripes. In both, the feeding organelles were 

 dedifferentiated and the animal rested within a flask-shaped cyst 

 with a gelatinous plug (Fig. 4). Only once have I seen coeruleus 

 apparently beginning encystment within a membrane inside which 



A 



B 



Fig. 4. Cysts of (A) coeruleus and (B) polymorphus. (After Stein, 



1867.) 



it rotated for a day but then died. In nigery however, cystment 

 seems to occur readily, with small, spherical, brown cysts, though 

 again, stentors have not yet been seen emerging therefrom 

 (unpublished). 



Altogether, stentors exhibit a considerable range of behavior 

 in their orderly swimming movements, avoiding responses, food 

 selection, and attachment or detachment of holdfast "at will". 



