A, resting stage, characterized by the presence of connective tissue, narrow tubules, few residual germ cells undergoing cytolysis. B, early gametogenesis stage, characterized externally by flat and colourless shape, and microscopically by visible presence of connective tissue, some growing follicles (less than 30% of examined area), few spermatozoa in the centre of some follicles. C, mature stage, characterized externally by thick, milk-coloured aspect, and microscopically by 90–95% of examined area covered by follicles, some fully grown, packed with spermatozoa, very little surrounding connective tissue. Scale bars: 100 µm.