are rare among other ciliates. Holotrich feeding hab- 

 its also explore many other ways of getting along in 

 the world. Paramecium hwsaria harbors green flag- 

 ellates, and it is said that the animal can survive on 

 its green cells if bacteria are not available. The 

 astomate (mouthless) holotrichs live in the digestive 

 tracts of annelids, the livers of mollusks, the body 

 cavities of annelids and crustaceans. Parasitic forms 

 with mouths raise pustules in the skin of fishes or 

 may be found on the gills of tadpoles. Many live as 

 relatively harmless commensals, sharing the food of 

 their hosts by taking up posts in the mantle cavities 

 of bivalve mollusks or the intestinal tracts of sea 

 urchins or mammals. 



THE SPIROTRICHS 



The spirotrichs have, leading to the mouth, a 

 downward-curving zone of membranelles, large tri- 

 angular plates of fused cilia that create powerful 

 feeding currents. Spirotrichs may be divided up into 

 heterotrichs. oligotrichs. and hypotrichs. according 

 to their patterns of ciliation. The heterotrichs are 

 covered all over with short cilia, and they include 

 such well-known forms as the huge, trumpet-shaped 

 stentors, named for the Greek herald in the Trojan 

 War. who, according to Homer, had a loud trumpet- 

 like voice. Stentor lives attached by the narrow end 

 of the "trumpet," but may detach and swim about 

 with the muscular body partly contracted. The large 

 blue species, Stentor coendeus. with the fully ex- 

 panded body showing alternate stripes of white and 

 blue from the white muscle fibers that underlie 

 the blue-pigmented layer, and with the large mem- 

 branelles of its feeding disk steadily wafting small 

 fiagellates and ciliates into the mouth, is one of the 

 finest sights in the animal kingdom. It is quite impos- 

 sible to leave the eyepiece of a microscope when such 

 an animal is performing. Also in this group is the 

 long, slender Spirostomiim. about the length of a 

 printed dash — and one of the largest of fresh-water 

 protozoans. Often seen in dark, shady pools, it may 

 when numerous whiten the surface of the water. 

 Balantidium coli normally parasitizes pigs but may 

 shift (when its cysts get into the food or drink of 

 people who handle pigs) to the human intestinal 

 wall, causing diarrhea. 



The oligotrichs have the body cilia reduced or ab- 

 sent. Such are Halteria, familiar to those who exam- 

 ine pond water, as the minute form that seems to 

 bounce like a ball across the field of the microscope; 

 the marine tintinnids that secrete about themselves 

 vase-shaped cases; and the many commensals of 

 hoofed animals, including the astoundingly complex 

 Epidiniiim ecaitdatum. 



The hypotrichs include many of the most com- 

 mon and most amusing ciliates that turn up in the 

 fresh and salt waters usually examined. Oval and 



.\ fiilK expanded large blue stentor, Stentor cocrulciis, 

 with membranelles beating around the edge of the 

 feeding disk. (P. S. Tice) 



