Structural and cytochemical features of the yolk globules and of the nucleolus in the growing oocytes of the mollusc Murex trunculus L.

A relationship between the second phase of the nucleolar activity and the variations which the yolk globules undergo in their staining affinities and in their chemical constitution has been found in growing oocytes o Murex trunculus. The results obtained enable us to recognize that the different staining affinities among the initial intermediate and definitive yolk granules correlate with the variations in their chemical constitution. The variations are due to the lack of proteins with disulfide groups, tryptophan, indolic and phenolic substances and tyrosine in the initial yolk globules, substances which, on the other hand, are found in both intermediate and final globules. Furthermore, the final globules are lacking in lipids. The presence of both acid and alkaline phosphatase activities is limited mostly to the initial yolk globules. It was possible to deduce from the chemical constitution in the nucleus of the oocytes under examination that the phase in which the nucleous modifies its content of chemical substances and when the transformation in the chemical constitution of the yolk globules occurs, is not coincidental. Both of these phenomena occur when vitellogenesis is advances although the nucleus undergoes vacuolization through out the time in which previtellogenesis passes to vitellogenesis. That the presence of the hydrolytic enzymes is correlated with nucleolar activity and that their probable role is connected with the yolk transformation and subsequent reconstruction is discussed.