Ultrastructural characteristics of the oocytes of A. robustus G.O. SARS in the early vitellogenic stages are studied. The different cellular compartments and their relationship with functions of synthesis and storage characteristic of this group are described. Blebbing processes of the outer lamina of the nuclear envelope related with the 'endoplasmic pool' and that, apparently. transport material from the nucleus are shown. A part of the cisternae of the endoplasmic reticulum undergo infolding in the cytoplasm, fuse and evolve, morphollogically, towards a particular type of yolk bodies. Some considerations are done about the possible mitocondrial origin of a part of the accumulation vesicles that appear scattered in the ooplasm of the same time that fenomena of degradation of the cristae of a part of the mitocondria are observed.