ABSTRACT
Females in stage 1 and stage 2 of the annual reproductive cycle were injected daily for 16 days with 1 µ1 of 2.5 × 10-7 M oestradiol-17β in 100% ethanol per g fresh weight. The injections of oestradiol-17β resulted in a significant increase of PAS-positivity and basophility in the oocytes and a decrease of the pyloric caeca indices compared with control individuals. The oocyte diameters of treated individuals appeared to be significantly larger than those of the controls. The frequency distribution of oocyte diameters from the treated individuals was significantly different from that of the controls. The maturation index of the treated individuals was 2.4, that of the controls was 1.4. Oocytes in the injected individuals were in a more advanced stage than in the controls. Injection of oestradiol-17β stimulated vitellogenesis. Since the treated individuals were more heterogenous with respect to the stages of the reproductive cycle than the controls, and because the diameter of the smallest oocytes were the same for both treated and control individuals, a minimum size of the oocytes is probably required before oestradiol-1 73 is able to affect the growth of oocytes. The increase of the PAS-positivity in the oocytes of the treated individuals demonstrates an incorporation of protein or other substances into the oocytes. The decrease of the pyloric caeca indices of the treated individuals suggests that these substances may originate from the pyloric caeca.
