314 GEORGE W. TANNREUTIIER. 



into many small bodies and disappears within the cytoplasm 

 leaving a clear unstained outline (Figs. 28-30), which is later 

 absorbed. The old macronucleus sometimes persists in the 

 exconjugants after the formation of the new micronucleus and 

 macronucleus are complete, before the beginning of its dis- 

 integration. 



Occasionally when the macronucleus of one of the conjugants is 

 situated at the anterior end in close proximity to the cytoplasmic 

 bridge as in figure fifteen, it would be carried over to the opposite 

 conjugant, due to the movement of the cytoplasm within. The 

 two macronuclei within the same conjugant however, pass 

 through the usual stages in their disintegration. This passing 

 over of the macronucleus through the cytoplasmic bridge from one 

 conjugant to the other is quite common in one of the species of 

 Chilodon, where its passage can be followed in the living forms. 

 In Chilodon, however, not only the macronucleus may pass in toto 

 from one conjugant to the other, but the macronucleus of either 

 conjugant divides, one of the resultant daughter nuclei acting as 

 the moving nucleus and the other as the stationary nucleus, 

 comparable to the micronuclear activities in normal conjugation. 



GENERAL REMARKS. 



Conjugation and binary fission of the ciliate P. griseus, to my 

 knowledge, has never been described. The general activities 

 however, in reproduction for the most part agree with the results 

 of investigators as found in other ciliates. 



One of the chief points of interest in studying the different 

 stages in the life history of the ciliate P. griseus, is the direct 

 association of binary fission and conjugation with encystment. 

 The entire process of cell division may occur within a given cyst. 

 While the first steps in conjugation always occur (as far as my 

 observations go), in the free swimming forms and encysts later 

 when the union of the two conjugants is complete. Temporary 

 encystment however, can not be considered as essential for binary 

 fission and conjugation. Since both may occur in the free forms. 

 Encystment here acts more as a protection in unusual or adverse 

 conditions. In no instance observed did the daughter cells pro- 

 duced by binary fission within the cyst, undergo conjugation 

 before their escape. 



