172 DONALD WALTON DAVIS 



the unlike bounding mesenteries were adjacent to each other in 

 the original animal, since pairs of mesenteries of different 

 character are rare. The apparent lack of agreement may be 

 due in some cases to a tearing from the esophagus of mesen- 

 teries previously complete or, in a single case (no. 18b, table 5), 

 to the fusion of an incomplete mesentery with th6 esophagus 

 during closure of the wound following fission. That complete 

 mesenteries should occasionally have their connection with the 

 esophagus broken is not remarkable considering the nature of 

 the process of fission. The possibility of the abnormal union of 

 an incomplete mesentery with the torn edge of the esophagus is 

 supported by the fact that, in early stages of regeneration of 

 cut specimens, atypical adhesions of parts are common. Such 

 adhesions seem much more rare in later stages, indicating that 

 regulation probably occurs. It is conceivable that an attach- 

 ment of a normally incomplete mesentery with the esophagus 

 might persist even though adhesions of other parts should be 

 eliminated. 



There remain four cases (pairs 3, 10, 15, and 22) in which the 

 most probable explanation of the disagreement is the complete 

 elimination of one or more mesenteries. It is possible that this 

 loss of mesenteries is due to the detachment during fission of a 

 minute piece which was overlooked and lost; chc it may be that 

 such a piece was partially separated from the larger ones, or 

 otherwise extensively damaged, during division and subsequently 

 absorbed. In support of the latter hypothesis may be mentioned 

 certain mesenteries found in a few specimens not represented in 

 the tables. These are mostly pieces regenerating after being 

 separated by artificial cuts. The abnormal mesenteries are at- 

 tached to the column wall, but not to the esophagus. They 

 extend through only part of the length of the column. The 

 mesogloea of these mesenteries is thick and stains heavily, but 

 the longitudinal muscles are feebly represented. They are cer- 

 tainly injured old mesenteries and are probably in process of 

 elimination. 



Summarizing the occasional irregularities adjacent to the plane 

 of fission, we may say that small mesenteries may be cut in two 



