400 



BIOLOGY OF THE PROTOZOA 



form stalked cysts within which they undergo a metamorphosis. 

 If hosts and cysts are eaten by an actinian the metamorphosed 

 ciliates are liberated and these take up life again in the gastral 

 cavity of the coelenterate. 



Of the endoparasitic forms the Pycnothricidae (Xicollelidae of 

 Chatton and Perard) are noteworthy because of the varying posi- 

 tions of the mouth, which is connected with an elongated furrow 



ti m 



Fig. 172. — Nicollellidae. Nicollella, Collinella, and Pycnothrix. (After Chatton 

 and Perard, Bull. Biol, de la France et de la Belgique, 1921; courtesy of Prof. X. 

 Caullery and Les Presses Universitaires de France.) 



running from the mouth to the anterior end. In Xicollela, Chatton 

 and Perard, the furrow runs to the mouth which lies at the middle 

 of the ventral surface; in Collinella, Chatton and Perard, it runs 

 to the mouth at the posterior end; while in Pycnothrix, Schubotz, 

 which is by far the largest of the parasitic ciliates (2 to 3 mm.), 

 it runs down the ventral surface, around the posterior end and 

 back to near the anterior end on the dorsal surface where the 



