Differentiation of Blenniids — STRASBURG 
for the low number of fin rays there. If the 
mutation acted to increase fin ray number 
then it would need to appear at both the 
northern and southern limits of the band of 
islands, again to explain the symmetry seen 
in Table 1. Because of the unlikelihood of 
these occurrences, as contrasted with the 
much more plausible temperature effects, mu- 
tation may probably be ruled out from the 
fin ray picture seen in the islands extending 
from the Marianas to the Gambiers. 
It is very likely that I. zebra , the Hawaiian 
form of edentulus , was derived from a stock of 
edentulus - like blennies which acquired a high 
number of fin rays because of the temperature 
effects here discussed. Because of geograph- 
ical isolation and mutation it subsequently 
evolved into its present form. Its lack of 
nuchal cirri, possession of a well- developed 
cephalic crest in females, and distinctive fin 
ray counts probably warrant its consideration 
as a full species. 
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