イワナ，Ｓａｌｖｅｌｉｎｕｓ　ｐｌｕｖｉｕｓ，のじょ骨およびじょ骨歯の成長について

It is well known that the form of vomer and distribution of vomerine teeth are used to indicate the interrelationship of genera in the Salmonidae. But the variation and the growth of vomer and vomerine teeth have not been sufficiently cleared until now.<BR>The form and the growth of vomer and distribution of vomerine teeth in the char, Salvelinus pluvius, are discribed and reported in this paper.<BR>The cleared and stained larvae indicate that ossification of vomer begins between 40 days old, about 21.1mm in standard length (SL) and 60 days old, about 22.3 mm SL. The small unpaired membrane bone in the larval stage, 22-23mm SL, do not have a posterior shaft.<BR>A very rapid growth of vomer takes place between 100 days old, 22.8mm SL and 120 days old, 38.7mm SL, and when the fish becomes about 39 mm SL, 120 days old, the vomer bocomes divided into an anterior part and a posterior shaft. The conical teeth begin to appear in the vomer from 50 days old to 100 days old, 22.1-22.8mm SL and when the fish is about 53.5mm SL, 150 days old, about five teeth are present on the anterior part.<BR>In the young and pre-adult char, the vomer is shaped like an inverted boat hull, with a dorsal flat and ventral crest. Most of the vomerine teeth are borne in a series along the lower edge of the anteri-or enlarged part, and the tapering shaft is toothless. Some specimens (23 %) have short median ridges which bear vomerine teeth arranged vertically in a single series. Five char (12.5 %) among 40 preadult char showed the vomer without teeth.