ASEXUAL REPRODUCTION IN SAGARTIA 197 



incomplete endocoels, except for absence of new 'bounding' 

 mesenteries. 



In the foregoing account, the determining influence of the old 

 bounding mesenteries has prominently appeared. This influ- 

 ence appears early, and finally results in an adjustment of old 

 and new parts that restores in the bounding region the normal 

 pairing of mesenteries of a given cycle, and, usually but not 

 invariably, the regular alternation of pairs of different cycles. 



In connection with the mesenteric formulas of regenerated 

 regions, a word of caution was given concerning assumptions of 

 homology between mesenteries bearing the same designation. 

 The reason for this may now be made clear. Mesenteries indi- 

 cated by the same symbol in different formulas (table 2, p. 191) 

 are similar in character, as directives or non-directives, in posi- 

 tion of the muscle banners (toward or away from the directive 

 plane), and in location with respect to other mesenteries. If we 

 retain these designations but place them in the order of their 

 development, we have the following as the chief formulas: 



No. la c\ d, c», c2 



No. lb c\ d 



No. 2a c\ d, c\ c\ c\ (1) 



No. 2b c\ d, c\ {1) 



Formula no. lb differs from no. la in the absence of mesen- 

 teries c^ and c^. In formula no. 2b the third mesentery is desig- 

 nated d^, but may really be homologous with c* of formula 

 No. 2a. In that case the reduction here also consists in the 

 suppression of c^ and c^ If this is correct, strict regard for 

 homology would require that the mesenteries labeled c^ in the 

 lower part of figure 11 and on the left of figure 13 should be 

 labeled c^ In one or two instances I have found mesenteries c^ 

 and c^ in a very early state of development when the other com- 

 plete mesenteries were united with the esophagus through the 

 greater part of its length. Whether these would have attained 

 full development or would have disappeared cannot be de- 

 termined. In either event these cases may represent a condition 

 intermediate between the more complete development and the 



