In order to examine gross-anatomical changes of the brain components of yellow-tail with their body-growth, an observation was made on the specimens of four stages, larval, young, immature and adult. Total number of the specimens used are 102, the total length of them ranging from 10mm to 1, 100mm.
The main results obtained are summarized as follows.
1) Most remarkable changes of the following two stages.
(a) Notable growth of each of the corpus cerebella, valvula cerebelli and eminentia granularis was observed in the fish of a transitional stage of their behaviour shifted from a rather planktonic life at the sea surface to a life travelling under floating seaweeds; total length of the fish at this stage was measured to be 30-50mm.
(b) Conspicuous growth of the corpus cerebelli, valvula cerebelli, eminentia granularis and crista cerebelli was found in the fish of the other transitional their behaviour shifted from a life travelling under floating seaweeds to free-swimming life; total length of these fish was 100-150mm.
2) These results suggest that in yellow-tail there exists an intimate correlation between the behavioural modification and the morphological changes of some brain components, especially of the corpus cerebelli and valvula cerebelli.
