No abstract

Synopsis An account is given of the development of the oöcyte in Nasonia vitripennis. The probable functions of the trophocytes, the accessory nuclei and the annulate lamellae are discussed.

Oogenesis is compared in two cheilostome bryozoans with contrasting reproductive strategies. from southern Britain: Chartella papyracea (Ellis & Solander) is a non–placental ovicellate brooder, whereas Bugula flabellata (Thompson in Gray) is a placental brooder. The ovarian cycles are similar, and each oocyte develops in tandem with a single nurse cell. Eggs of both species are telolecithal, However, those of B. flabellata are less than 20% the volume of those of the other species, and there are considerable differences in the ultra‐structure of oogenesis. In both cases, spermatogenesis has the typical bryozoan pattern. Precocious insemination of the oocyte occurs in both species.

Oögenesis in the oviparous marine teleost, Blennius pholis L., is examined. Eleven developmental stages are identified by ultrastructural observations when changes in the distributions of the organelles and inclusions are described. An exogenous source for the protein yolk precursors is indicated, but less clear is the endogenous contribution. Changes in the follicle epithelium are described together with the formation of the zona which is considered to be follicular in origin. Two types of follicle cell are distinguished and these probably function differently in the process of zona formation. The zona becomes divided into the externa and interna, the latter probably resulting from the chemical ordering by disulphide bonding of the proteinaceous material of the former.

No abstract