Abstract
The migration of the germ cells into the mammalian gonad and their subsequent differentiation has been the subject of many investigations and controversies. However, sufficient facts have accumulated which led Witschi (1962) to state that ‘the formerly controversial subject of the origin and unbroken continuity of the germ cell lines can now be considered settled’. Histo-chemical techniques for alkaline phosphatase have made it possible to selectively stain and identify primordial germ cells (McKay, Hertig, Adams & Danziger 1953; Chiquoine 1954; Mintz 1959). The path and development of the germ cells has been described in detail in histological investigation (for review see Brambell 1956; Mintz 1960; Franchi, Mandl & Zuckerman 1962) and recently labelling techniques have made the continuity of the germ cell line ‘visible’ (Rudkin & Griech 1962; Peters, Levy & Crone 1962; Kennelly & Foote 1966; Borum 1966; Peters & Crone 1967).