CRICKET EMBRYOS IN 3D
A brief contribution to 3D photography
by Robert Sturm, Salzburg (Austria)
As I could demonstrate in a contribution previously published in Micscape, embryogenesis of Orthopteran insects such as grasshoppers or crickets is commonly characterized by a multiplicity of developmental stages. As shown in the sketch below, embryonic development of the Orthoptera (in the concrete case: Locusta migratoria) commonly starts with the fertilized oocyte (= egg cell), which undergoes an extensive process of cell division. This procedure results in the production of a multiplicity of new cells, which subsequently grow and differentiate into those organs needed for the next developmental stage. The embryogenesis of insects represents a specificity insofar as early egg cleavage only involves nuclear subdivisions, which are not accompanied by respective partitions of the cytoplasm. This phenomenon is commonly known as so-called syncytial or superficial cleavage. The first terminus is derived from the fact that cells containing a high number of nuclei form a syncytium. The second terminus indicates the fact that this specific development mainly takes place near the surface of the egg cell.
After extensive formation of several thousand cell nuclei, these cellular compartments are subjected to a migration process, during which they move towards the egg periphery and produce a layer containing a multitude of cell-like structures (energids). Among scientists this layer is known as blastoderm, which itself may be subdivided into the germ band or ventral plate, the initial stage of the embryonic body, and the serosa forming the yolk sac. The germ band defines the origin of the embryonic body and is subsequently subjected to an extensive process of differentiation, which results in the mapping out of the fundamental body plan of the insect. The germ band undergoes a continuous enlargement, in the course of which the three germ layers (endoderm, mesoderm, and ectoderm) are formed. From these histological units different insect organs emerge during the essential processes of histogenesis and organogenesis. After completion of tissue and organ development, the differentiated embryo undergoes a procedure of intense stretching, muscle contraction, and uptake of gas into the tracheoles. The final stage of embryonic development is characterized by the hatching process, where the animal comes out of the egg.