466 GARY N. CALKINS 



spects, for example in the power of encystment and of conjugation. 

 Conjugation epidemics occurred in all of the experimental 

 series and many preparations were made, but these have not 

 yet been critically studied. Ex-conjugants from the experi- 

 mental series gave rise to series in which all the characteristics 

 of any ex-conjugant series were manifested (e.g., X7A series). 



There is very little evidence to indicate that the stage of 

 maturation during which the conjugating pair were cut had any 

 effect upon the after results. The process of normal conjuga- 

 tion extends over a period of approximately twenty-four hours. 

 Judging from the number of times a given stage is found in 

 fixed and stained preparations, it is evident that the stages lead- 

 ing to the first maturation require the longest time and the 

 stage of the second maturation division the shortest time, while 

 the period of the third nuclear division and migration of the 

 pronuclei is again a long one. The majority of the thirty pairs 

 that were successfully cut were in the stage of the first maturation 

 division and the majority of the remainder were in the final 

 stages of conjugation. The PXl series, the VXl series, and the 

 VX2 series all started from individuals which were cut while in 

 the parachute stage of the first maturation division. The 

 PX6 and PX7 series were derived from individuals cut in the 

 stages of the second and third maturation divisions, respectively. 

 The X75 series came from an individual cut during a late stage 

 in conjugation when the two. wandering pronuclei were passing 

 each other at the anterior end. This experimental individual 

 thus had the stationary or female pronucleus ready for the 

 mate that never came, since both migrating pronuclei were 

 removed by the operation of cutting. The VX3 series came 

 from an individual cut after the wandering pronuclei had passed 

 each other and the male and female pronuclei were almost 

 ready to unite; that is, amphimixis was assured. The XZ2 

 series, finally, came from an individual which was cut immediately 

 after separation subsequent to amphimixis. 



The differences and resemblances in relative vitality and 

 characteristics of the life-cycles of these different experimental 

 series are too slight to justify a conclusion that cutting at differ- 

 ent stages of conjugation had anything to do with them. 



