SEARS CROWELL 



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Fig. 11. Profile sketches of the morphogenesis of an isolated early hy- 

 dranth bud of Campanularia. The finally differentiated disk consists of 

 little more than a hypostome surrounded by a full circle of tentacles. The 

 outer line represents the secreted perisarc; the tissue is stippled. 



buds of Campamdaria, however, showed an extraordinary ability to 

 continue to perform the activities ordinarily performed by the 

 distal-most tissues of a normally developing hydranth. They gradu- 

 ally spread themselves laterally, laying down externally the hydro- 

 thecal perisarc, and they continued to do so until a hydrotheca of 

 ordinary size was produced. By this time the tissue itself was only 

 a thin disk at the position where hypostome and tentacles would 

 differentiate in a whole bud. Then the disk differentiated into just 

 these distal-most parts. 



The whole process just described proceeded much more slow- 

 ly than is the case in normal development. If one were dealing 

 only or mainly with cell migration it would be expected that the 

 events could occur at nearly normal speed. The slowness suggests 

 that new cells are being produced, as is believed to be the case 

 in ordinary hydranth development, and old ones are being de- 

 stroyed and utilized. Regardless of the validity of this sugges- 



