CELL MOVEMENT, RATE OF REGENERATION, AND THE AXIAL GRADIENT IN TUBULARIA

Abstract

1. The regeneration process in Tubularia is divisible into two phases. There is a period of tissue movement, during which extra cells are provided to the presumptive regeneration site, followed directly by the period of differentiation of the new hydranth. 2. Differences in rate of regeneration between narrow versus wide stems, the distal versus the proximal ends of stems ligated in the middle, and apical versus basal stem levels are all due to differences in the time occupied by the tissue movement. 3. Narrow and wide stems differentiate at the same rate, as do the distal and proximal ends of stems ligated in the middle. However, pieces from basal stem levels differentiate, in these experiments, at a significantly greater rate than pieces from apical stem levels. 4. Both rate of regeneration considered as a whole and rate of differentiation vary from colony to colony and between comparable stems taken from the same colony. 5. Neither the tissue movement nor the process of differentiation is always continuously progressive. Reverses in the direction of movement and spontaneous dedifferentiation of the differentiating primordium have both been observed. 6. The differentiation process is continuously dependent upon a critical cell density in the primordium. Evidence is presented that differences between stems in the movement of the tissue during the differentiation process represent the only systemic factor responsible for variations in differentiation rate among similar stems from the same colony. 7. The tissue movement is due to the movement of the amoeboid cells of the ectoderm, and the axial gradient, as manifested by an apico-basal decrease in rate of regeneration, is a reflection of the apico-basal gradient in the rate of tissue movement. 8. Both the apico-basal gradient in oxygen consumption and differences in oxygen consumption during regeneration correlate perfectly with the rates of tissue movement at different levels of the stem and with the period during which the movement occurs. It is inferred that differences in oxygen consumption indirectly measure the differences in tissue movement, which is an aerobic process.