Studies on the Pronephros of Cirrhina mrigala (Hamilton)

Abstract

The paper deals with the structure and the degeneration of the pronephros in Cirrhina mrigala, an Indian carp. The earliest stage that was available for the study was the free swimming larva measuring 6 mm in total length. At the 6 mm stage the pronephros of C. mrigala is fully formed. It reaches maximum size at 10 mm stage. The stages between 11 and 15 mm may be regarded as transitional stages when the functional pronephros becomes non-functional. During this period the pronephric corpuscle becomes isolated from the pronephric tubules and the haemopoietic tissue and is progressively reduced in size. It is not absorbed by the pronephric haemopoietic tissue. The degeneration of the pronephric tubules is a slow process when compared with that of the pronephric glomerulus. The embryonic development of the pronephros in teleosts has been described by several workers (Swaen et Brachet, 1899, 1902; Audige, 1910; Stroer, 1932; Mahon and Hoar, 1956; Rangarajan, 1957; and Ford and Newstead, 1958). It is an established fact that the pronephros in teleosts is a transient larval organ except in a few species in which it persists throughout adult life (Balfour, 1882; Guitel, 1906, 1908; Gerard, 1941; Fraser, 1950; and Rangarajan, 1957). Descriptions of the exact mode of the involution of the teleostean pronephros are available only in isolated instances (Cole and Johnstone, 1901; Audige, 1910; and Ford and Newstead, 1958). Though detailed information about the mode of degeneration of the pronephros of Teleostei is relatively rare, Pavlenko (1916), Maschkowzeff (1926) and Fraser (1927) have described the development as well as the regression of the pronephos in three species of Sturgeons Acipenser sturio, A. stellatus and A. rubicundus respectively.