THE RÔLE OF THE FIN RAYS IN THE REGENERATION IN THE TAIL-FINS OF FISHES

IN FUNDULUS AND GOLDFISH

¹ GENERAL EDUCATION BOARD FELLOW IN BIOLOGY, BROWN UNIVERSITY

1. Regeneration is faster from the level of the cut that exposes more fin-ray cross surface. The difference in arrangement of the fin rays in the tails of Fundulus and goldfish accounts for the rate of growth being faster or slower at opposite regions of the two types of tails.

2. Regeneration from square holes cut in the tails of fishes shows that a reversal of growth of the rays from the posterior face of the hole is possible. Healing in the longitudinal faces and repairing of the injured rays take place. Regeneration takes place only from the cross-cut ends of fin rays. The reversed rays are of the same branching pattern as the distal portion from which they are produced; that is, the same pattern that a cross cut would regenerate posteriorly from that level.

3. When rays that normally would grow into the lobe of the tail are displaced into the central portion of the tail of a goldfish, they are not "held back" by any tension in the center of the tail. The rays continue to grow and form abnormal lobes in the central portion of the tail.

4. Correlation between size and branching is brought out by two types of cuts. (a) A cut surface anterior to the scaly base of the tail in Fundulus regenerates "abnormal" rays. The shape of the tail can thus be changed from rounded to straight, and persists as such for more than seven months. (b) An oblique cut at the point of doubling of rays in the goldfish exposes more cross surface than a straight cross cut. The regenerate from such a surface has produced a third set of branches instead of two sets, as would be typical in the goldfish used.

5. There is a minimum size of all rays in a particular kind of tail, and the size is apparently equal for all the rays.

6. The evidence herein presented suggests that the fin rays are self-differentiating structures.

(a) The initiation of growth is due to cutting the fin rays crosswise.

(b) Rate of growth seems to depend on the amount of exposed surface of the fin rays.

(c) Cessation of growth appears to be due to the attainment of the minimum size of the ray at which no further growth takes place.

(d) Form of the tail appears not to be associated with pressure or tension relations but with the mode of branching of the fin rays and hence their size and the formative influences that they possess.