GENERAL CONSIDERATIONS 31 



to a virile condition. This may be repeated upwards of 300 times, until 

 reorganization, if it occurs, is ineffective and the protoplasm dies. Thus 

 the macronucleus, like all other derived structures of the cell which 

 come from the euplasmatic substances, apparently has a limited potential 

 of activity. But the macronucleus may overcome this difficulty through 

 the more deeply reaching phenomena in the life history, viz., endomixis 

 and conjugation. 



Reorganization by Endomixis and by Conjugation 



In isolation cultures of any ciliate, if the extra individuals which 

 remain over after the daily isolation is made on any day are put into 

 a larger container with abundant food, a so-called "encystment test" 

 or "conjugation test" is started. In my experiments these are begun 

 regularly every ten days. Here the individuals multiply by division until 

 there are thousands in the container. In the early stages of the life cycle 

 of U. mobilis all such individuals die of starvation, but in a month 

 or six weeks after the initial conjugation from which the series is 

 started, such tests result in an increasing number of encystments. A 

 type of breakdown which is not seen in the division phenomena is now 

 manifested. The macronucleus is fragmented, and the fragments are 

 distributed in the protoplasm where they ultimately disappear, while 

 a new macronucleus is formed from a product of micronuclear division. 

 Other structures of the derived organization are resorbed, waste matters 

 and water are voided to the outside, and a cyst membrane is formed 

 within which the organism may remain in a partially desiccated condi- 

 tion for months. When it is recovered from the cyst and reestablished in 

 isolation culture, it has an optimum vitality and passes through a com- 

 plete life cycle exactly like that of an ex-con jugant. This phenomenon 

 of endomixis, except for encystment, is the equivalent of endomixis 

 in Paramecium aurelia as originally described by Woodruff and Erdmann 

 (1914). Endomixis thus brings about a more far-reaching and more 

 complete reorganization than does division; the new macronucleus aris- 

 ing from a micronucleus, is provided with a new potential of vitality. 

 For an up-to-date account of endomixis, see Woodruff, injra, Chap- 

 ter XIII. 



An interesting phenomenon which I interpreted as analogous to endo- 

 mixis occurs in the ciliate Glaucoma (Dallasia) jrontata (Fig. 11). At 



