FORM-REGULATION IN CERIANTHUS. 121 



SUMMARY. 



1. Supplementary partial discs with a number of tentacles cor- 

 responding to that portion of the whole circumference which 

 they represent can be produced from lateral transverse cuts in the 

 body-wall of Ccriantlins. 



2. If the lateral cut is in the cesophageal region and is deep 

 enough to involve the oesophagus the supplementary disc pos- 

 sesses a mouth because the cut surfaces of the body-wall unite 

 with the cut surfaces of the oesophagus, thus forming a second 

 opening into the oesophagus. If the cut is below the cesophageal 

 region the supplementary disc possesses no mouth. In the 

 extreme aboral region of the body the formation of supplementary 

 discs does not occur. 



3. When the lateral cut is made in the cesophageal region the 

 permanent collapse and atrophy of the tentacles and region 

 directly above the cut occurs, or if these have been removed their 

 regeneration is retarded and atrophy occurs after a time. This 

 collapse and atrophy is due, not to loss of intracellular turgor 

 but to decrease in the internal water-pressure since the enteric 

 cavity of the region above the cut is completely shut off from the 

 general enteric cavity and from the exterior. 



4. In two cases the formation of tentacles on the aboral end 

 of a piece of certain form was observed. In both of these cases 

 the conditions of internal pressure were apparently similar to 

 those which exist at the oral end, but the less rapid regeneration 

 of the aboral tentacles indicates either a difference in structural 

 relations at the two ends or a difference in " polarity." 



HULL ZOOLOGICAL LABORATORY, 



UNIVERSITY OF CHICAGO, 



December, 1903. 



