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THE BIOLOGY OF HYDRA : 1961 



ferentiation appears in such shaken cultures when the population 

 density is around one Hydra per ml., all Hydra being fed and 

 cleaned once per day. 



This is our present approach to this fascinating problem. When 

 completed it should be possible to place Hydra in a running stream 

 of chemically treated water and have them turn sexual even 

 though all feedback between them and their culture water has been 

 eliminated. Figure 4 shows our apparatus for conducting such an 

 experiment. It was used to show definitively that increased levels 

 of pC02 alone were not sufficient to induce sexual differentiation 

 in Hydra littoralis, the conclusion being that other feedback factors 



Fig. 4. Set of six syphons that allow 1-5 Hydra (in small beakers at 

 lower end of syphons) to be maintained in a flowing stream of chemically 

 known water with all feedback effects removed. The rate of water flow is 

 varied by the size of the hypodermic needle used as well as by the level 

 of water within the large bottles. A liter of BVC culture solution is added 

 to each bottle daily and the air space flushed out for five minutes with 

 whatever COo-Oi-N . mixture one desires. 



