PRIMORDIUM IN RELATION TO STRIPE PATTERN l8l 



characterized by fine striping lies adjacent to an area bearing wide 

 stripes. The fine stripes need not be to the right of the wide, as is 

 normally the case, but can lie to the left in an arrangement which 

 is just as effective. Yet in the reverse arrangement the direction of 

 coiling is reversed, as if the anlage always bends away from the 

 wide stripes and into the fine, even though this results in a primor- 

 dium of reversed asymmetry. And finally, it is evident that the 

 wide- and fine-stripe areas are able to interact even though 

 heteropolar. 



One of the most convincing demonstrations of the correlation 

 between primordium formation and locus of contrasting stripe 

 widths (l.s.c.) was provided by splitting the fine line area of the 

 primordium site by introducing a narrow sector bearing wide 

 stripes. Now there were three loci of stripe contrast, the original 

 primordium site and on each side of the implanted patch, and on 

 regeneration three anlagen were produced, one in each Ls.c.(d). 

 In further development the two primordia on the left usually 

 joined to form a V-shaped anlage which might not form mouth- 

 parts. It should be added that control tests showed that neither a 

 mere splitting of the fine-line zone nor the implantation there of 

 an additional fine-line sector had the effect of producing super- 

 numerary primordium formations. 



Many other types of graft were made to produce juxtapositions 

 of wide- and fine-stripe areas in all possible combinations, and 

 these are also illustrated in Fig. 46. They showed that primordium 

 formation is always correlated with this juxtaposition but is 

 independent of the orientation of the striping; for in addition to 

 the modifications already mentioned, the contrasting stripes may 

 lie at right angles, or abut end to end homopolar or heteropolar. 

 This shows not only that the two types of area can interact regard- 

 less of orientation but also implies that the developing oral cilia 

 and their kinetosomes are autonomous in their precise alignment 

 into membranelles, because normal membranellar bands were 

 always produced regardless of the^ disposition of the adjacent 

 ectoplasmic striping. For example, when anterior halves of 

 regenerators were rotated 180° on their posterior halves (g) 

 membranellar differentiation which was to all appearances normal 

 occurred at the new l.s.c. where the lateral- striping lay at right 

 angles to the primordium instead of roughly parallel to it. 



