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TJniversity of California Publications. [Zoology 



the stem, which is more rapid than the elongation of the hy- 

 clranth. Snch a factor, however, does not explain how the 

 naked ectoderm, which occupies one-eighth the length of the stem 

 at the stage shown in Fig. 27, comes to occupy, in contraction, 



Fig. 26. a, Optical section of larva with six proximal tentacles. 

 Stumps of two tentacles shown. X 120. h, larva with three distal and 

 four proximal tentacles. 



more than half the length of the stem in the full grown adult. 

 This extension of the naked area may be due in a small measure 

 to the more rapid growth of this portion of the stem ; I have no 



