Regeneration time at the different levels of hydra.

1. Regeneration time of the hypostome increases progressively from the oral to the aboral direction. Converse is true for the basal disc. More time is required to form basal disc from aboral-oral direction. 2. In absence of both terminal determinants, the time of regeneration of hypostome and basal disc in a longer piece is less than that of a smaller middle piece; regeneration time in the smaller fragment takes more time. 3. Inhibitory effect of hypostome on the formation of a basal disc has been evidenced in which a slight faster rate of basal disc regeneration is possible in absence of the hypostome in the full length of hydra. 4. In smaller pieces, slower rate of hypostome regeneration is noted in absence of basal disc at posterior regions of the oral end. 5. Hypostome lengthens the time of formation of basal disc in its vicinity, whereas basal disc accelerates the formation of a hypostome in its nearby. Hypostome determining influence is stronger than its counterpart and can act from a greater distance. 6. Determination on hydra has been explained on the basis of an interaction between the relative developmental potential of the participating cells at a given level and the strength of the diffusible communicating system originating from the regions of physiologically active area of hypostome.