REGENERATION IN HYDRA ATTENUATA 



577 



Table 5. 



TRF (Tentacle Régénération Factor). Mean values for the Tentacle Régénération 

 Factor (TRF > 0) at the various axial levels in each of four clones of standard animais. 

 Values omitted from statistical considération are in brackets. JBT=Just Below Tentacles. 

 N=Number of Regenerated Animais for which the TRF > 0/ Number of Regenerated 

 Animais. 





Clone 7a ? 



Clone 6 ? 



Clone 18 3 Clone 3a ? 



JBT 



N = 



208 ± 127 



21/25 



206 ± 82 

 10/13 



154 ± 84 

 9/10 



183 ± 69 

 13/15 



75% 



N= 



229 ± 139 

 13/21 



188 ± 70 

 6/16 



193 ± 84 

 9/12 



194 - 82 

 9/12 



50% 



N= 



203 ± 113 

 16/21 



262 ± 84 

 7/17 



140 ± 71 

 9/16 



247 - 48 

 8/12 



25% 



N = 



175 ± 88 

 10/20 



192- 58 

 6/9 



(78 ± 17) 

 3/10 



137- 44 

 5/8 



10% 



N= 



0/3 



137^ 100 

 5/7 



(133 ±6) 

 3/5 



(200) 

 1/5 



(d) Discussion 1 



From the foregoing it may be concluded that (1) there are, in the absence of 

 presumed inhibiting structures, inhérent différences in the régénération performance 

 of the given axial régions, (a conclusion also reached by Burt (1934) for Pelmato- 

 hydra ;) but that (2) thèse levels do not stand in ranked relation to one another in 

 a linear or steadily declining gradient; Thus, JBT régénérâtes hydranths faster 

 than either the 75 % or the 50% level but both 75 % and 50% regenerate at about 

 the same time. Also the final number of tentacles regenerated by the levels in the 



1 Mookerjee and Sinha (1967, Roux' Arch. f. Entwick.mech. 158: 331-340, System of 

 Stability and Lability in Hydra). cite évidence that basai plate and hypostomal tissue appear to 

 be mutually incompatable : grafts of basai plate in the vicinity of the hypostome are rejected, while 

 tentacles implanted into basai plate régions fail to induce complète hydranths. A System of two 

 equipotential tendencies is postulated in accordance with the classical théories of détermination 

 given above: The two unipotential tendencies merge into a bipotential midregion representing 

 a mutual compétition between the two fields of détermination. Once again, inhibitor substances 

 are invoked to explain the transition from the " original equipotential System into two distalo- 

 proximal déterminations " (p. 338). 



