UROLEPTUS MOBILIS ENGELM. 451 



fusion in conjugation offers an exceptional opportunity for 

 cutting, for, uniting by the anterior ends, the free bodies extend 

 outwards hke the two arms of a V. A successful operation cuts 

 the V at the apex, giving two pieces if the cut is in the long 

 axis, or three pieces if the cut is transverse. One of the arms 

 (and the apical piece if the cut is transverse) is immediately 

 fixed and stained. The other arm representing the second 

 individual of the pair is placed in fresh culture medium and 

 maintained in the same manner as a normal ex-conjugant. The 

 processes of nuclear change are synchronous in the two individ- 

 uals, hence the permanent preparation furnishes a picture of the 

 nuclear apparatus with which the experimental animal starts. 



Not only is it difficult to cut the individuals in the desired 

 plane, but, succeeding in this, it is difficult to carry them through 

 the period of reorganization during which mortality is high. 

 Many successful cuts were useless because of loss of the fixed 

 individual. Thirty successful cuts, however, were made; of 

 these the cultural fragment died at the end of forty-eight hours 

 in two cases; one died at the end of five days; one at the end of 

 six days; three in seven days, one in eight, two in nine, and three 

 in eleven days; two in twelve, two in thirteen, and two in four- 

 teen days, while eleven reorganized perfectly, and of these, seven 

 completed the full life-cycle. 



During my absence from New York in 1920 and on many 

 other occasions the cultures were carried on by my colleague, 

 Professor Louise H. (aregory, and I take this opportunity to 

 express my appreciation of her careful work and my gratitude 

 for her continued interest and help. 



RESULTS 



The first material to yield a successful operation was obtained 

 from the P series in its 135th generation. Conjugations were 

 abundant in a conjugation test on April 19, 1919. One pair was 

 successfully cut, and the two fragments began to reorganize. 

 One of these died, but the other completed its reorganization 

 in seven days and was estabhshed in culture on the 27th of April 

 1919, as the PXl series (fig. 1). 



