Studies on echinoderm oogenesis.―I. Antedon bifida (Pennat)

Abstract

The fully-grown eggs of Asterias rubens and Antedon bifida are almost identical in constitution, each containing yolk spherules, smaller droplets of fat, mitochondria and Golgi bodies. They agree also in the relation of the Golgi apparatus and mitochondria to yolk formation. In each the mitochondria show the usual changes. The Golgi apparatus of the oogonium and young oocyte consists of 1 or 2 scales at the sides of the nucleus. The scales increase in number and are scattered to the periphery of the egg. Yolk granules arise on the concave sides of the scales. In Antedon, cup-like groups of scales are formed, within which yolk granules develop. The function of the Golgi apparatus apparently is that of initiating the isolation of the preformed yolk out of the cytoplasmic solution. A yolk nucleus occasionally appears in the egg of Antedon only, and seems to have some secondary relation to formation of fat. It is suggested that the yolk nucleus is the result of accumulation of nucleolar material owing to its excessive extrusion, and that it does not appear in the eggs of Asterias owing to the material being used up as fast as formed. There is some evidence of extrusion of nucleolar material in solution in both eggs. Experiments on living eggs of Antedon with neutral red and brilliant cresyl blue have demonstrated that the vacuolar system arises under the influence of the Golgi bodies, which can be seen in vivo, in much the same way as yolk droplets arise. There is no relation between yolk and vacuome, however, the latter probably being a reaction of these cells to the dyes.