The development and degeneration of the mesonephros of the sheep is described with particular reference to the curious glomerular structure occupying the cranial one-third of the organ and here referred to as the giant glomerulus.

The giant glomerulus and in particular the cranial two tubules draining it on either side provide useful landmarks whereby corresponding regions may be compared at different ages. An attempt is made to analyse the factors which determine the form and relations of the definitive glomeruli and tubules. These factors include the early relations of the somitic stalks and nephrogenic cord, the precocity of growth and vascularization of the preglomerular tissue and the degree of overcrowding and overlapping of the tubule primordia.

The cellular activities of the mesonephric tubules are described and discussed and the view is upheld that these are of a peculiar secretory nature.

The processes occurring in degeneration are outlined and the absence of the massive cranial degeneration described by Felix in man is commented upon.