Abstract
The gonad, buccal cavity, gill, esophagus, salivary gland, intestine, liver, kidney, fat column, and eye were studied histologically during growth of the brook lamprey, Lampetra reis-sneri. Gonads of all individuals showed ovary-like structures at about 70 to 90mm in total length.In females, oocytes continued to grow.In males, oocytes degenerated, and a tiny testis originated from a small number of residual undifferentiated germ cells.Upon histological observation, the sex was easily determined in individuals larger than 120mm in total length.Initial tooth develop-ment (intraepidermal keratinization) occurred at stage 5 of metamorphosis.Esophagus of the adult type was distinguishable by stage 5.The salivary gland and its duct were also formed by stage 5.Intestine and kidney degenerated during metamorphosis.The liver of tubular gland type changed to the adult type by stage 3.In ammocoetes larvae, main hematopoietic tissues were located in intestine and kidney, but in adults they were found in the fat column.
