Ultrastructural Observations of Vitellogenesis in the Spider

Ovaries from the spider crab, Libinia emarginata L. were studied to learn more of vitellogenesis in crustaceans. Oogonia and previtellogenic oocytes were found in the core of the ovaries. Vitellogenic oocytes are located more peripherally. Profiles of the endoplasmic reticulum are abundant in the vitellogenic oocytes. The granular and agranular reticulum as well as the Golgi complex are active in yolk synthesis. As vitellogenesis proceeds, yolk precursors are incorporated into the egg by micropinocytosis at the egg surface. Thus, in Libinia, yolk materials appear to be derived from both intraand extraoocytic sources. Cytologists have long been interested in the sources of yolk precursors and the mechanisms by which they achieve their definitive forms within the oocyte. The means by which yolk is formed varies among different groups of animals. Such diversity is particularly well documented in the phylum Arthropoda. Recent investigations of numerous insects have implicated extraoocytic sources of yolk materials and activities of the oocyte surface in the vitellogenic process (Anderson, 1964; Roth and Porter, 1964; Stay, 1965; Telfer, 1961). In the crustaceans, there is some evidence of an extraoocytic origin of yolk precursors (Kerr, 1966) as well as active yolk formation by organelles within the oocyte itself (Beams and Kessel, 1963; Kessel 1968). Since the crustaceans have been less extensively studied than the insects, the present investigation of oogenesis in Libinia emarginata was undertaken to learn more about vitellogenesis in this group. MATERIALS AND METHODS Immature females and mature females brooding eggs of Libinia emarginata (L) were obtained from the Marine Biological Laboratory, Woods Hole, Mass. Ovaries were fixed for 90 min in either Karnovsky's (1965) paraformaldehyde-glutaraldehyde mixture or 2.5%,, glutaraldehyde in 0.1 M phosphate buffer. Tissues were washed in 0.1 M phosphate buffer and postfixed in buffered 1 OSO 4, pH 7.5. After dehydration through graded concentrations of ethanol, tissues were infiltrated and embedded in Araldite. Sections, stained with uranyl acetate (Watson, 1958) and lead citrate (Venable and Coggeshall, 1965), were examined with a Philips 300 electron microscope.