Pinocytosis in the developing egg of Limnaea stagnalis L.

Abstract

In 1946 Raven, working with sections of Limnaea eggs, described numerous vacuoles appearing in the ectoplasm at the 40 cell stage. Their content was strongly eosinophilic and with all stains used the colour of the vacuole content corresponded to that of the egg capsule fluid surrounding the egg. During the development of the egg the albumen vacuoles became larger and larger, occupying at the 120 cell stage a large part of the ectoplasm. Also at the 40 cell stage small conical or hemispherical vesicular protrusions could be observed on the surface of some blastomeres. Others had the appearance of small thickened rings of variable diameter, protruding slightly above the surface of the cells and surrounding a crater-like field. At the 120 cell stage their number had increased considerably and 40-60 of such ringlets were observed in most eggs. Since the formation of the ringlets corresponds in time to the absorption of albumen by the cells, Raven put forward the hypothesis that they represent inlets destined for the ingestion of egg capsule fluid by the developing egg. In order to test this hypothesis it seemed worthwile to study these structures by electron microscopy.