76 THE BIOLOGY OF STENTOR 



rupture in the surface of the cell as Schuberg (1890) first thought, 

 for even with the most drastic manipulation of dividers no gaping 

 or separation occurs along the fission lines. Yet it is reasonable to 

 suppose that there is a severing of the granular stripes and fibrous 

 structures in the clear stripes, because we know that the striping 

 also has a strong tendency to heal together when cut and this 

 procHvity would have to be overcome. The severance is, however, 

 not necessarily irreversible. Popoff (1909) described one case and 

 I have seen another in which division was aborted and the fission 

 line disappeared without a trace, showing the pigment stripes 

 again running continuously from pole to pole. 



All that we can be certain of at present is that the pigment 

 granules are moved away at the levels where the colored stripes 

 cross the future furrow. Something of how this occurs may be 

 shown in the aboral longitudinal half of a stage-4 divider which 

 still continued on its course and attempted division. As shown in 

 Fig. I 6a, the granules at mid-level in each stripe were seen in one 

 place to have shifted from the center of the stripe posteriorly and 

 this may have been the prelude to the complete depigmentation of 

 the stripes in the adjacent region. This appearance resembles that 

 of stripe multipUcation, and it is possible that new, short, posterior 

 kinetics were being introduced which pushed the pigment granules 

 aside as they formed double rows of cilia demonstrated by Randall 

 and Jackson for the new tail pole. The half-cell did not complete 

 division, but it did form a secondary tail-pole, very likely because 

 the body striping remained severed. This case is also significant 

 in showing that although the furrow normally begins at the 

 anterior end of the oral primordium this is not essential to furrow 

 formation. 



The fact that the fission line does not form all at once but 

 progresses in two directions around the cell suggested to Weisz 

 (1951b) that there are two waves of dissolution, each beginning at 

 one point on a given stripe and spreading radially until it touches 

 and sets off a new center of dissolution in the next adjacent intact 

 stripe, like the firing of a fuse. This would not explain, however, 

 why the fission line moves sharply posteriorly on one side of the 

 primordium; nor why, in Stevens' (1903) observation of longitu- 

 dinal halves of dividing stentors, the furrow stopped short by two 

 pigment stripes on each side of the line of heal; nor why the line 



