THE ANNUAL CYCLE IN THE TESTIS OF THE EASTERN BROOK TROUT, SALVELINUS FONTINALIS (MITCHILL)

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Abstract
The annual cycle in the testis of the eastern brook trout can be divided into six stages. A histological description is given of each of these stages and of the structure of the gonad. Primordial germ cells are always present in the lobules and so provide a permanent source of spermatogonia. The lobule boundary cells remain quiescent throughout a major part of the reproductive cycle, but become highly vacuolated during the latter half of the period of functional maturity. During the period of involution, phagocytes invade the seminiferous lobules and efferent ducts and ingest the residual sperm. The typical glandular interstitium of higher vertebrates is not present in this species. A gland-like structure is contained in the sperm duct, of which the function is unknown at the present time.