No. 3.] MORPHOLOGY OF THE STENTORS. 477 



S. roeselii endures confinement better than the Blue Stentor, 

 and I have kept specimens for months under seemingly very 

 unfavorable conditions. They sometimes multiply to some 

 extent in aquaria. The food consists largely of bacteria. 



4. Stentor polymorpJms (Miill.), Ehrbg. 



The specimens of this species which I have studied do not 

 differ in any important respect from the typical ^. polyniorpJnis 

 of Europe. I found them in sparing numbers at Williamstown, 

 and an immense colony at Worcester. This colony is estab- 

 lished in a slow stream, from one-and-a-half to four feet in 

 depth. The bottom is covered with large angular pebbles and 

 small boulders. There is almost an entire absence of all except 

 microscopic vegetation. For a distance of 100 yards the Sten- 

 tors are attached to the stones in such numbers as to give to 

 the whole bottom a mottled green appearance. 



I have found not a single specimen of ^S. polyinorphus entirely 

 free of zoochlorellae, although some from Lake Quinsigamond 

 contained very few, and appeared pure-white to the naked eye. 



Although little inclined to multiply, this species bears 

 confinement better than any other Stentor with which I am 

 acquainted. One often finds them in very old gatherings that 

 have stood in the laboratory for months. 



5 . Stentor cceruleus, Ehrbg. 



This beautiful species is in all probability as widely diffused 

 as the ubiquitous S. polymorphus, but seems to be more 

 restricted to particular localities. With the exception of a very 

 few found in Ouisset Pond, Falmouth, and a few from Wolf 

 Lake, South Chicago, 111., my specimens have all come from 

 Alewife Brook, Cambridge, where the species has multiplied 

 exceedingly under rather peculiar conditions. Alewife Brook 

 receives the sewage of a portion of North Cambridge, and also 

 the escape-water from the engine of the pumping-station of the 

 Cambridge Water-works. The water from the pumping-station 

 warms the brook to such a degree that for a distance of 100 

 yards below its influx the brook freezes over only in the coldest 



