342 S. O. MAST 



At first union is very weak so that the conjugants can readily 

 be separated by squirting them out of a pipet. Later they be- 

 come so firmly united that they cannot be separated without 

 injury. The conjugating pairs continue to swim about, but 

 their movements are, owing to their relative position, neces- 

 sarily more or less uncoordinated. Usually one proceeds for- 

 ward for a time and then the other. Thus they rarely get any 

 considerable distance from the place where union occiirred. 

 The duration of the union varies greatly. It depends largely 

 upon the temperature. Occasionally, pairs are found which 

 never separate. But at room temperature, they usually re- 

 main united only about twenty to thirty hours. During this 

 time there is nuclear transfer similar to that found in Para- 

 mecium (Prandtl, '06). All of the steps involved in this process, 

 degeneration of macronucleus, divisions of micronucleus, etc., 

 occur after the union of the conjugants takes place. Whether or 

 not there is anything in the nature of nuclear reorganization in 

 conjugants which are artificially separated is not known. 



The ex-con jugants usually begin to feed about one hour after 

 they separate. Then, after growing rapidly for about two hours, 

 they divide, after which they proceed as usual. If they are not 

 allowed to feed after conjugation occurs they do not divide. 

 Nor do they encyst. Some of them live a week or more but all 

 invariably die without fission if they are not fed. This was 

 repeatedly observed and it was found to hold without exception. 



The discovery that ex-conjugants die if they are not fed 

 greatly facilitated the process of continuing, for a long time, pedi- 

 gree cultures without conjugation; for such cultures were at 

 different periods maintained in the encysted state, and it was 

 often difficult to obtain cysts without at the same time having 

 conjugants which were difficult to eliminate before it was known 

 that they die if they are not fed. 



The elimination of food, subjection to optimum temperatures 

 and the presence of numerous individuals in a small space 

 facilitate conjugation just as it does in Paramecium (Jennings, 

 '10). This process, however, often occurs in the presence of 

 much food with very few (4 to 8) individuals present, and it 



