EXPERIMENTS WITH CHRYSOMELID BEETLES

Abstract

1. If the region of a freshly laid egg of Leplinotarsa decemlineata, which contains the germ cell determinants (Fig. 1, gcd), is killed with a hot needle and these granules are thus prevented from taking part in embryonic development, the embryo produced by the rest of the egg lacks the germ cells. This supplements former experiments in removing the germ cell determinants, and indicates that these granules really determine the germ cells. 2. When the primordial germ cells of Leptinotarsa decemlineata are killed in the blastoderm stage (Fig. 2, pgc) the resulting embryos lack germ cells. This is the earliest known stage in which surgical castration has been performed among the Insecta. 3. When the anterior or posterior parts of freshly laid eggs (Fig. 1) are killed, the material remaining alive develops that part of the embryo which it would have produced if the eggs had remained intact (Fig. II). No regeneration of the part which would have been produced by the killed region takes place. 4. If the anterior or posterior parts of eggs in the blastoderm stage (Fig. 2) are killed, the resulting tissue represents the parts of the embryos which would have been produced by the living material if the entire egg had been allowed to develop (Figs. 8 and 9). 5. When parts of young embryos (Fig. 4) are killed, the remaining tissue develops normally (Figs. 15-18). Even small pieces of tissue (Fig. 17, tf), which are widely separated from the rest of the embryo, continue to develop normally. 6. Parts of old embryos develop up to the time of hatching. There is no regeneration of the killed part by the living tissue. 7. The eggs of Leplinotarsa decemlineata, at the time of deposition (Fig. I), are definitely oriented with respect to the future position of the embryo.1 The areas of the peripheral layer of cytoplasm (Fig. 1, khbl) are already set aside for the production of particular parts of the embryo, and if these areas are killed, the parts of the embryo to which they were destined to give rise will not appear. Likewise areas of the blastoderm(Fig. 2, bl) are destined to produce certain particular parts of the embryo.