Experimental Studies on the Developing Perch (Perca flavescens Mitchill)

Abstract

The records of experimental analyses of the embryogenic processes in the Teleost are comparatively meagre. The results of defect-experiments performed on Fundulus eggs by Morgan, 1 Lewis, 2 ,³ and Hoadley 4 indicate that the ultimate limitation of cellular potencies occurs during gastrulation, but they supply no conclusive evidence concerning the nature of the mechanisms whereby the limitation is accomplished. The time is now ripe for experimental investigation and analysis of Teleost development in the light of the modern concepts of experimental embryology.

The eggs of the yellow perch were used for experimental material in the present research. Transplantation of the tissue corresponding to the dorsal lip of the amphibian blastopore induces the formation of a secondary embryo; the experiment and results are comparable to those of Spemann 5 on the egg of Triton.

The cytoplasm of the perch egg is large in amount in comparison with the yolk. The germ-ring forms and gastrulation commences when almost one-half the yolk is covered by the blastoderm. Early in gastrulation the lip of the blastoderm at which invagination is principally localized induces the formation of a secondary embryo when transplanted to an extra-embryonic region near the germ-ring of an egg the same age as the donor. The induced embryos are only slightly smaller than the normal, and have been obtained complete as far anterior as mesencephalon and myelencephalon. The parts formed are perfect. Active motility and vigorous heart-beat developed in the oldest induced embryo. The primary embryos are normal.