No. 3-] MORPHOLOGY OF THE S TEN TORS. 507 



zooids now takes place in the path marked out by the fission- 

 line. I cannot agree with Schuberg's view that the constric- 

 tion is accompanied by a rupture of the pellicula. He says: 

 " Bel Stentor nun muss . , . ein Durchreissen schon friiher 

 [than in other Infusoria] stattfinden, oder mit einem Wort 

 die ganze Diirchschnunmg ist von Anfang an mit einem Reissen 

 der Pellicula in bestimmter Richtung verbunden." Now, any 

 rupture of the pellicula occasions a protrusion of the cytoplasm 

 whenever the animal contracts, notwithstanding the strong 

 tendency of the integument to close over every wound. Since 

 no protrusion of cytoplasm is visible along the line of fission, 

 it seems very doubtful whether the pellicula is actually rupt- 

 ured. Longitudinal sections of Stentors in the middle and 

 later stages of fission show no evidence of a rift in the pellicula. 



Although I do not consider it a rupture of the pellicula, I 

 have not come to a satisfactory conclusion in regard to the 

 nature of the fission-line. It certainly divides the substance 

 of the blue stripes (ectoplasm), and so produces a white line 

 around the body, not unlike one of the clear stripes. Sec- 

 tions show that the line is superficial, and not the optical 

 expression of a plane passing through the animal, as in ordinary 

 cell-division. . I have sometimes thought that a contractile fibre 

 of extreme fineness was developed in close connection with 

 the pellicula, which, by contracting, brought about the con- 

 striction in the manner of a string passed around a yielding 

 body and tightened. The supposed fibre, however, may be 

 merely the sharp fold in the integument, caused by constriction. 



From the study of preparations I feel confident that the 

 myonemes are not cut by the fission-line, but simply become 

 bent sharply inward (Fig. 34). Until a late stage of fission 

 the stripes on either side of the line remain very accurately 

 matched (Figs. 31-35), notwithstanding the notable narrowing 

 of the stripes at the posterior end of the distal individual. 



At this point a series of remarkable changes in the position 

 of the new frontal field and adoral zone begin, and proceed 

 rapidly until the completion of fission. Hitherto the plane 

 of the new frontal field has remained nearly parallel to the 

 surface of the Stentor. It now begins to project more and 



