GEORGE \V. TANNREUTHER. 



takes place in the exconjugants. But if we isolate an equal 

 number of the exconjugants that encysted during conjugation, 

 and an equal number of those that failed to conjugate immedi- 

 ately after encystment. We find that the rate of fission per given 

 number is about the same in the two isolated lots. Hence it may 

 be safe to conclude that simultaneous encystment and conju- 

 gation do not produce renewed vigor or at least increase the 

 fission rate in P. griseus. 



FIG. 31. Prorodon griseus in the early completion of the permanent cyst with 

 all the organs in tact. 



FIG. 32. Later stage of encystment with the disappearance of the cilia and the 

 breaking up of the pharynx. The micronucleus and the contractile vacuole(?) 

 persist. The macronucleus is in its early stage of metamorphosis, c. v., contractile 

 vacuole. 



FIG. 33. The macronucleus in its later stage of metamorphosis. Several 

 cytoplasmic vacuoles are present. 



FIG. 34. Final stages of metamorphosis of macronucleus or cytoplasmic 

 reorganization of structures during encystment. The missing organs have re- 

 formed. The new macronucleus is a direct metamorphosis of the old. 



Encystment in the ciliates according to Calkins may serve a 

 threefold purpose. That is for protection, reproduction and 

 reorganization. In P. griseus there are two types of cysts which 

 we have designated as thin or temporary and thick or permanent. 

 The two types differ in the thickness and the compactness of their 

 walls. The temporary cysts are quite flexible and yield to the 

 moving ciliate within. The temporary cyst serves two purposes: 

 first for protection against sudden adverse conditions such as 



