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THE BIOLOGY OF HYDRA : 1961 



quick regeneration which followed removal of the hypostome and 

 most of the tentacles in a small young hydranth of Cordylophora. 

 An analagous operation, illustrated in Figure 10, was performed 

 several times on hydranth buds of Campanularia. Both the excised 

 piece and the part which remained proceeded to differentiate just 

 as they would have if no operation had been made. The isolated lit- 

 tle pieces consisted of little more than tentacles and a hypostome. 

 Such little creatures captured Artcmia larvae and passed them into 

 the hypostome. They lived unchanged for about four days— a nor- 

 mal life span for an unnourished hydranth. Similarly the "half hy- 

 dranths" still on the colony showed normal activity but no restitu- 

 tion of the missing tentacles. 



fh hr5 



Fig. 10. The left half of the upper portion of a late hydranth bud of 

 Campanularia is cut off. Both parts differentiate just what they would have 

 produced normally, and there is no later restoration of missing parts. 



In another series of experiments we cut off and isolated very 

 young hydranth buds of Campanularia, as shown in Figure 11. These 

 were of such small mass that it would be impossible for them to 

 develop a normal hydranth. Had these been athecate hydranth buds 

 one would have predicted that they would produce either nothing, 

 because of the small size, or at best a tiny hydranth. These isolated 



