Using the early embryos of Agelena opulenta, the cell migration along the surface of the embryo was examined. It was especially investigated whether the cells migrated inward through the central region of the germ disc. The central region of the germ disc is generally called blastopore or primitive groove. The embryos were immersed into liquid paraffin and were filmed one frame per two minutes with a 16mm cinemicrographic apparatus attatched on a compound microscope. The cell migration was analyzed in detail on the cinefilms. The cells being distributed along the area to a little upper of the equator at the stage of germ disc formation were observed migrating towards the germ disc during the early development. When those cells arrived at the margin of the germ disc they further migrate towards the blastopore moving over the germ disc, then at the blastopore these cells disappeared among the cells of the germ disc. Probably the cells migrated inwards penetrating the cell layer of the germ disc at the blastopore. During this migration most of the cells divided once. The inward cell migration at the blastopore was clearly perceived on the film at the stage when the posterior cumulus started its migration toward the equator.
The instars of spiders have usually been determined by measuring the carapace widths. Rearing experiments using three kinds of preys, however, indicated that individual variation in the carapace widths of Xysticus saganus was much larger than that in the length of posterior eye row (LPR), and the frequency distribution of the carapace width for each instar overlapped considerably between different instars. Therefore, more reliable determination of the instars can be made by use of the frequency distribution of LPR, which were not affected by the difference in sexes or food conditions.