REGENERATION IN HYDRA ATTENUATA 



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formance, as may be seen from the data. (Compare Tables 1, 2, 3, 4, 5 and 6 and 

 Figures 2, 3, 4, 5, and 6.) 



Regenerating animais were kept at room température (21°C. — 23°C). Experi- 

 ments were performed continuously throughout the year, with the exception of 

 the month of July. 



An animal is considered as having begun to regenerate a hydranth when one 

 or more tentacle buds are apparent under a 24 fold magnification. See Figure l. 

 A basai plate is considered as having been regenerated when the animal is observed 

 able to stick to the glass surface of the bowl. 



Where applicable, régénération performance was evaluated according to the 

 following criteria, arbitrarily selected as measurable expressions of speed and size 

 of the regenerate: 



1. The time of tentacle régénération (TDT): The time needed, after cutting, 

 for the onset of hydranth régénération (as defined above). 



2. The time of basai plate differentiation (BDT): The time needed, after 

 cutting, for the complète régénération of a basai plate (as defined above). 



3. The initial tentacle number (ITN): The number of tentacles observed in the 

 first protocol period. This does not refer to the number of tentacles initially laid 

 down, which because of the method of protocoling was not necessarily observed. 



4. The final number of tentacles (FTN): The number of tentacles observed in 

 the last period of protocol. This refers only to the number of tentacles observed 

 120 hours after cutting and not to the final number regenerated, which because of 

 the method of protocoling was not necessarily observed. (The mean number of 

 tentacles for 17 standard animais from mothers selected at random from the 

 four laboratory clones was 5.87 ±0.5.) 



5. The final tentacle number minus the initial tentacle number (FTN-ITN): 

 The différence between the final tentacle count and the initial tentacle count shows 

 whether there are axial différences in the increase in tentacle number. 



6. The tentacle régénération factor (TRF): The factor is defined as = 



where / is the number of new tentacles formed in a given unit of time, u. 

 It ranks animais regenerating a larger number of tentacles in early protocol 

 periods higher and reflects the considération that an animal regenerating a tentacle 

 in the first unit of any given régénération period is thought to be faster than one 



(b) Evaluation Procédures 



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