PRIMORDIUM IN RELATION TO STRIPE PATTERN 193 



Although primordia form at sutures where wide-stripe areas 

 He heteropolar to fine striping (Fig. 46H), local reversing of the 

 wide-stripe half of an l.s.c. completely blocked anlagen formation 

 and no regeneration occurred though the specimens lived for a 

 week or longer (i). 



These apparent exceptions may point up the fact that the 

 correlation between primordium formation and loci of contrasting 

 pigment stripe widths is a purely empirical one. It is probable 

 that the granular stripes as such have nothing whatever to do 

 directly with primordium formation. They contain no kinetosomes 

 as possible progenitors of the basal bodies of the primordium. 

 Instead of narrow-stripe areas we might just as well have spoken 

 of close-together areas, referring to the fact that the clear stripes 

 with their kinetics here are not so far apart and their opposite 

 would then be " wide-apart areas " (cf. UhUg, 1959). At stages i 

 and 2, in fact, the anlage arises wholly within the fine-line zone 

 which is not an area of stripe contrast, but the point is that this 

 place is near a wide-striped area and that experiments show this 

 to be significant. All we can say is that there is a condition which 

 is usually associated with the juxtaposition of areas bearing wide 

 stripes with areas bearing narrow which is conducive to primor- 

 dium formation. In the exceptions to the rule this crucial condition 

 may well be present though not in its normal association with 

 contrasting stripe widths. Yet the whole question of interaction at 

 the l.s.c. still remains to be explored. 



It is attractive to regard the wide-stripe areas as inducing 

 primordium formation in fine-stripe areas adjacent or near by. 



G. Two stentors grafted at right angles. Anlage develops in 

 the only intact primordium site but extends in suture toward 

 remnant of membranellar band along locus without contrasting 



stripes. 



H. Regeneration primordium in narrow sector grafted to a 

 divider. At stage shown the division anlage is developing, while 

 the grafted one extended to form two membranellar bands 

 separated by a granular stripe an^ surrounded by uniform 

 medium-width striping. (Further development shown in Fig. 



41 J-) 

 I. Wide-stripes alongside primordium site reversed in place 

 and no primordium formation occurred though the specimen 

 survived for a week without mouthparts. 



