568 



GABRIELE KASS-SIMON 



The experiments themselves were performed on " standard " animais derived 

 in the following manner: Asexual animais bearing well-developed buds were 

 removed from their clones and placed in individual bowls 2 cm. deep and 5 cm. in 

 diameter, together with three or four Daphnia and/or Cyclops (hereafter referred 

 to as units of food). The Daphnia and Cyclops were obtained from the local pet 

 shop. After a 24 hour period, the detached buds were removed and in turn placed 

 in individual bowls, together with one unit of food each. Cutting took place 24 hours 



APPEARANCE 

 OF HYPOSTOME 



OR 



APPEARANCE OF 

 TENTACLE - BUDS 



Fig. 1. 



Early stages in hydranth régénération. Régénération considered as having begun at stage C. 



after feeding; the consumption of food being checked prior to opération. No food 

 was given thereafter. Protocol was made every eight hours during the first 48 hours 

 after cutting; after which it was taken every 24 hours for another three days. 



Paraffin-filled acetabula served as operating dishes. Millimeter graph paper 

 shallowly embedded in the paraffin permitted the animais to be measured during 

 cutting. Animais were transected with a scalpel (No. 1 1 blade) and viewed through 

 a stereo-microscope during transection. 



Although points of section vary according to the experiment, they are con- 

 fined to the following sites along the axis of the animal: Measuring upwards from 

 the basai plate, at Just Above the Basai Plate (JAB), at 10% of the animal's total 

 length, at 25% at 50% at 75% and Just Below the Tentacle Ring (JBT). (Because 

 the variance in length is great, no absolute measurement is possible for hydra.) 

 The sites are depicted in Figures 2 and 5. Animais are eut only once and the part 

 to be regenerated discarded ; the resulting différence in the sizes of the regenerating 

 pièces do not appear to have an effect, in themselves, on the régénération per- 



