FORM REGULATION IN CERIANTHUS .ESTUARII. 



37 



September 2j. — I. Marginal tentacles on most distal portion 

 5-6 mm. in length, decreasing to slight elevations on the opposite 

 side (Fig. 10). 



II. Marginal tentacles 2-3 mm. in length about the whole 

 margin (Fig. 11). 



Later the tentacles on the oblique piece underwent a gradual 

 equalization and the disc lost its obliquity as in oblique pieces of 

 C. solitarms. 



This series shows very clearly, and my other series afford 

 similar results, that tentacle-formation is accelerated on the more 



distal portions and retarded on the more proximal portions of 

 the oblique piece as compared with transverse pieces. 



Since internal pressure is in general so important a factor in 

 tentacle-formation in CeriantJms it seems not at all improbable 

 that the differences between the oblique and transverse pieces may 

 be due to local differences in the internal pressure in the oblique 

 pieces. The currents passing orally in each interseptal chamber 

 enter the inrolled portion of the oral end and, as was suggested 

 in my earlier paper, local differences in the internal pressure may 

 be produced by these currents since the body-wall is always 



