Early egg contractions and patterned parasynchronous cleavage in a living insect egg.

Abstract

Fifteen movements of egg ooplasm occur prior to the formation of the embryo of the beetle,Callosobruchus maculatus. These movements are associated with nuclear division taking place before formation of the embryo. Yolk globules exhibit a coordinated pattern of saltation and quiescence with these movements. The significance of this yolk activity for the movement of nuclei within the yolk mass is discussed. During the syncytial blastoderm stage the surface of the egg is infolded around the surface nuclei. Nuclear division during this period appears to produce localized stretching of the surface which in turn results in a "yolk contraction". Division is parasynchronous and patterned with a wave of anaphase configurations spreading across the egg. The significance of such "mitotic gradients" to patterning of insect segments is discussed.