The timing of changes in several internal organs during metamorphosis of anadromous larval lamprey Petromyzon marinus L.

A current scheme for identification of stages in metamorphosis of sea lamprey Petromyzon marinus makes use of external features (Manion and Stauffer 1970). Of 13 larvae (ammocoetes) of anadromous sea lamprey sacrificed before they exhibited the earliest (stage 1) features of metamorphosis, 11 showed differentiation of the adult kidneys, and the beginnings of regression of the larval alimentary canal and endostyle. These changes are initiated not more than 1 month nor less than 1 week before known external signs are evident. There is a need for a reexamination and a further description of the early phases pf lamprey metamorphosis. Metamorphosis in anadromous sea lamprey provides excellent potential as an experimental system in comparative developmental biology.