PRIMORDIUM IN RELATION TO STRIPE PATTERN 189 



Fig. 50. Consequences of minimum contrast in granular 

 stripe widths. 



A. Graft of halves of two stentors with fine-stripe areas 

 removed. After delay of 19 hours two primordia finally formed 



in the sutures with very minor stripe contrast. 



B, No regeneration without stripe contrast. Aboral side with 

 medium-width striping is isolated by a cut but left attached to 

 oral portion so that the latter, in swimming will draw out the 

 aboral fragment and keep it from folding. The parts soon 

 separate. Last sketch shows fragment which failed to regenerate, 

 presumably because it lacked a l.s.c, though it lived and was 



active four days. 



but primordium formation occurs before. Weisz (1951b) ascribed 

 the delay to time required for the transformation of the ciliary 

 row next to the widest stripe into a stomatogenic kinety, but there 

 is no evidence for a key kinety in normal oral differentiation. 

 Instead, it may well be the case that minor l.s.c. are quantitatively 

 less potent in exciting primordium formations and therefore do 

 so more gradually, and further evidence for this surmise will be 

 given in the next section. If so, a quantitative time factor would 

 be available for investigation in connection with anlage induction 

 by l.s.c. 



An attempt has been made to p^roduce nucleate longitudinal 

 fragments which are so narrow as to contain no significant contrast 

 in stripe widths (Tartar, 1956c). A longitudinal cut was made far 

 to the right of the central axis of a stentor but the two parts were 

 left joined at the tail pole. This was in order that the larger portion 

 by active swimming would draw out the smaller and prevent it 



