1 62 



FLORENCE PEEBLES. 



L and R) have been observed for days after the operation, 

 swimming about rapidly but showing no sign of fission, or of 

 regeneration of the lost end. Although the conjugating pairs 

 were cut at the same level after separation one fragment was 

 almost always smaller than the other (Fig. n). The small one 

 (R) generally dies, and the large one (L) divides to form a normal 

 race, when both halves lived the smaller one finally divided 

 and after many generations the descendants regained the normal 

 size. The fission of all fragments of conjugating pairs was 

 regular; I have never seen a large and a small cell formed by 

 division in the original plane as so frequently happens when cells 



12 



10 II 



FIG. 10. Conjugating cells showing region of the cut. 



FIG. 11. The right and left halves of a conjugating pair after removal of the 

 anterior end. 



FIG. 12. Left and right halves of a conjugating pair grafted together. 



are cut in the vegetative condition. This regularity would indi- 

 cate that the division plane is lost during conjugation, and that 

 when it is re-formed it is laid down in the center of the fragment. 

 In three of the operations the halves were pressed together so 

 firmly by the edge of the knife that the fragments grew together 

 at the cut surfaces. These grafted fragments (Fig. 12) showed 

 great activity for a few days, but finally died without dividing. 

 One of these was stained to see the nuclear condition. There 

 was a large single nucleus in each half. If these grafts could be 

 kept and fission induced, the regulation would, no doubt, be of 

 value in throwing light on the problem of the "nucleus-proto- 

 plasm-relation." 



F. The Effect of Cutting Cells Shortly after Fission. 

 In order to obtain cells at a definite period in their develop- 

 ment they were removed from the stock culture, and as soon as 



