Blastoderm development in honey bee embryogenesis as seen in the scanning electron microscope

Summary

Based on observations in the scanning electron microscope, we describe the successive changes at the cell surface of fertilized honey bee eggs which, over a period of 20 h, lead to blastoderm formation. Each change starts in the differentiation center located in the anterior egg half and from there spreads as a wave towards both poles. However, one of the waves is heterogeneous: the protrusions or caps of oolemma which start enveloping the preblastoderm nuclei arise in different ways in the anterior third and in the more posterior regions of the egg cell. After the formation of these protrusions, three mitotic waves pass over the peripheral nuclei. The last of these blastemal mitoses results in a two-layered arrangement of peripheral nuclei, each surrounded by an outpocketing of the egg cell basally confluent with the central yolky part. This two-layered state after some time transforms into a single layer of columnar outpocketings which increase in height by extending their borders centripetally into the secondary periplasm (inner ‘Keimhautblastem’). The outpocketings disconnect from the central yolk mass as separate blastoderm cells only a short time before gastrulation. The events described here consume nearly 40% of the time period between oviposition and hatching; thus, and by comparison with most other insects, blastoderm formation in the honey bee is a very lengthy process.