BUDDING AND LOCOMOTION IN THE SCYPHISTOMAS OF AURELIA

¹ From the Hopkins Marine Station of Stanford University and the Scripps Institution of Oceanography

The processes of budding and locomotion have been studied in a scyphozoan polyp, presumably the scyphistomas of Aurelia. It has been found (1) that the buds which develop near the hydranth of the polyp are quick to pinch away from the polyp (except for a connecting strand of ectoderm) and to migrate away by means of pedal stolons; whereas the buds which develop near the polyp's base may long remain attached. This indicates an opposition between the hydranth of the polyp and the bud.

(2) The stolons which develop at the upper end of the stalk of the polyp are quite commonly organs of locomotion as well as of attachment. They elongate, attach by their tips, contract, and so draw the polyp forward. The new stolon becomes the new base of the polyp, while the old base becomes drawn out and finally breaks from its attachment. The fact that new stolons form away from the base and away from the older stolons indicates an opposition between base and young stolons.

(3) The entoderm apparently plays the primary rôle in the formation and differentiation of buds, and in the formation, contraction, and final resorption of pedal stolons. Entodermal cells of the stalk of the polyp rearrange themselves into a solid core as the stolon elongates; they actively migrate back into the stalk as the stolon contracts.

(4) Small pieces taken from any region of the polyp show some power of regeneration. In general, there is a decline in hydranth-forming potentiality from the upper to the lower end. Pieces from the hydranth (oral disc and circle of tentacles) are irreversibly determined to form parts of a hydranth. Pieces from the body or stalk may regenerate whole polyps, although the relative size of the regenerated hydranth decreases as the base is approached. Base-forming tendency is strongest at the lower end. The power to form pedal stolons is greatest in pieces from the upper stalk.

(5) Small pieces of ectoderm only may round up and regenerate whole polyps. Pieces of entoderm round up but do not regenerate. Pieces including both ectoderm and entoderm regenerate in a manner typical of the region from which they are taken. The entoderm is thus the seat of irreversible invisible differentiation (chemo-differentiation).

(6) Various operations were performed on pedal stolons and upon the polyps which produce them; such as fragmentations of the polyp, and injury, isolation, fragmentation, and ligation of the stolons. The results indicate (a) that new stolons commonly grow from portions of the polyp's stalk farthest from the base and opposite the remains of older stolons, also on the side opposite a lateral wound; (b) that the outgrowth of a stolon is a self-determined morphallactic process independent of the polyp proper but dependent upon the presence and activity of a free and uninjured "tip"; (c) that contraction immediately follows in a part of a stolon when the phyalological continuity between the part and the tip is interrupted.

(7) It is suggested that the formation of the specialized ectodermal tip of a stolon is the result of an induction originating in underlying entoderm; and that the tip having thus originated acts as an organ of internal secretion in producing a "growth hormone." The hormone diffusing into the entoderm causes the entodermal cells to arrange themselves as the solid core of a stolon. The secretion of the hormone ceases when the specialized cells of the tip come into contact with the substrate and discharge externally.