ABSTRACT
A method is described for using a reflecting microscope to irradiate small precisely located areas of insect embryos with lethal micro-beams of ultraviolet light, so that cell lineages may be traced from histological studies of subsequent development.
The gamete precursors in Drosophila melanogaster were shown to be those pole cells which are carried into the posterior mid-gut rudiment during gastrulation. The interblastodermal-migrating pole cells are not incorporated into the embryonic gonad but probably play a role in the formation of mid-gut epithelium. The mesodermal rudiment of the gonad is derived from the posterior half of the mid-ventral mesodermal invagination, and is formed independently of precursor gamete cells. Bilaterally and unilaterally castrated flies resulted after pole-cell irradiation.
Support for certain parts of Poulson’s anlagen plan of the Drosophila egg was obtained from studies of development after irradiation of certain areas of blastema and blastoderm. The non-cellular blastema stage was more easily damaged by ultra-violet radiation than the blastoderm stage. Gastrulation was a critical stage, but the study supported Sonnenblick’s ideas concerning the morphogenic factors governing endodermal invagination. No departure from mosaicism was noticed, except that the results indicated some slight regulative capacity in the presumptive pole-cell area at the 1-hour stage.
