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J. S. HUXLEY AND G. R. DE BEER 



derm cells are smaller, and the most distal ones have lost the 

 typical disc-like structure. They are rounded and have lost their 

 serial arrangement in a single row : at the tip it is difficult to dis- 



Text-fig. 3. 



Campanularia. a. Stage 3. No trace of tentacles or liypostome. 

 Considerable new growth from the stem, b. The same zooid 

 magnified to show its change of shape. The dotted outline was 

 drawn one minute later than the firm outline, c, Tip of the 

 new growth from the same specimen in expanded condition. 

 d, The same specimen contracted two minutes later. The 

 ectoderm near the tip is attached to the perisarc ; proximal to 

 this the contraction is clearly visible, ect., ectoderm ; en., endo- 

 derm ; p., perisarc. (Camera lucida.) 



tinguishthem from the ectoderm cells, which have come to present 

 the same spheroidal appearance. PI. 26, fig. 7, is a photograph 

 of a single section showing progressive loss of differentiation 



