Ultrastructure of the yolk substance in preimplantation embryos of the gerbil. 
The yolk substance or deutoplasm in preimplantation embryos of the Mongolian Gerbil was observed to be composed of tubule-like structures which were grouped in slightly wavy bundles running in various directions and occupying the major cytoplasmic space in the cell.  The tubules were about 70 nm wide and, where cut longitudinally, had a maximal length of 2 micrometer in the micrographs.  This deutoplasm structure has no similarity to that observed in other species, thus supporting the earlier assumption that the ultrastructure of deutoplasm is species specific.