Fig. 4. In vitro effect of estradiol (E2; 10-6 mol
l-1) and E2 given in combination with melatonin (mel;
10-6 mol l-1, 10-9 mol l-1 or
10-12 mol l-1) on the mast cell number after 6 h of
incubation in testis of frogs captured in October. Vertical bars indicate
means ± S.D. Different letters (a versus b)
indicate significance at P<0.01.