1050 THE STRUCTURE OF EVOLUTIONARY THEORY
different covariance set, expressed on the fourth axis of this analysis (as discussed
previously), effectively all interregional difference arises from the operation of the
jigsaw constraint—as generated by minor differences in whorl sizes promoted to
substantial overall phenotypic effect through the allometric consequences of Cerion's
ontogenetic channel, so long as average adult shells, as they do in this case, reach the
same final size.
Note, in Figure 10-9, the separation of polygons for Aruba, Eastern Curasao and
Western Curasao by the first and third axes that express the jigsaw constraint, while
each polygon shows a similar extension along the second axis, representing the
different and separable component of intraregional (and ecophenotypic) variation in
mean shell size. Figure 10-8 shows characteristic shells for the regions. Note the
jutting apertures from Bonaire (second row) and, especially, the contrast, built by the
jigsaw constraint, between many-whorled specimens from Aruba in the top row
(longer relative residence in the second allometric phrase which, distinctively in
Cerion uva, induces an absolute narrowing in later whorls, leading to a "barrel" shape
for the entire shell, fat in the middle and narrowing at both ends)—and the fewer
whorled, but same sized, specimens from Western Curasao in the third row (which
pass less of their ontogeny in the second "barrel" phase and therefore do not become
constricted towards the end of growth, as in the Aruba specimens).
10 - 9. Minimum convex polygons drawn around the multivariate means for samples in each
region. The ecophenotypic factor of size makes no distinctions as each polygon becomes
elongated along this second axis, and as the truly larger fossil shells from Aruba occupy a
separate position at the high size end of this spectrum. But the first and third axes express the
jigsaw constraint, and the defining regional geographic variation within this type species of
the genus achieves clear expression in the separation of polygons on these axes.