Über die deutschen SüßwasserpolypenHydra fusca L.,Hydra grisea L. undHydra viridis L. Eine biologische Vorarbeit, zugleich ein Beitrag zur Vererbungslehre

Immortality and Pearl's Survivorship Curve for Hydra

“…1) implies potential immortality by indicating a constant mortality rate, independent of age ; that Pearl plainly pointed this out in relation to the curve he originally derived for Hydra (Pearl and Miner 1935) from the data given by Hase ( 1909) ; and that Pearl seems to have been among the first to suggest the potential immortality of Hydra on the basis of these data. 1) implies potential immortality by indicating a constant mortality rate, independent of age ; that Pearl plainly pointed this out in relation to the curve he originally derived for Hydra (Pearl and Miner 1935) from the data given by Hase ( 1909) ; and that Pearl seems to have been among the first to suggest the potential immortality of Hydra on the basis of these data.…”

“…Hase himself declared (Hase 1909) that he could not state the cause of death of his animals with certainty; that he had known hydras to live longer than the maximum life span observed in this experiment; and that this particular study was preliminary and exploratory. Hase himself declared (Hase 1909) that he could not state the cause of death of his animals with certainty; that he had known hydras to live longer than the maximum life span observed in this experiment; and that this particular study was preliminary and exploratory.…”

“…: those animals are immortal whose life span exceeds the patience of the investigator." Hase (1909) suggested that the advent of sexuality might affect physiological vigor and length of life. Child (1915) found that individuals newly separated from the parent were distinctly more susceptible to cyanide treatment, although developing buds were no more susceptible than the parent and might actually be more resistant.…”

Ecology of Pelmatohydra oligactis in Kirkpatricks Lake, Tennessee

“…DURATION or LIFE In 1936, Pearl and Miner presented a complete life table for Hydra fusca (P. oligactis) based on data for life durations given by Hase (1909). The mean duration of life for P. oligactis was computed as 54.89 days.…”

“…The mean annual standing crop on the bottom, although based on few samples, is 106 hydras per square meter. This mav appear to be a large number per square meter of bottom, but the mean annual standing crop on twigs, Hase ( 1909). The mean duration of life for P. oligactis was computed as 54.89 days.…”