194 DONALD WALTON DAVIS 



mesenteries destined to become complete almost invariably 

 appear. One, lying nearer the bounding mesentery and de- 

 veloping for some time slightly in advance of the other, becomes 

 the mate of the old complete bounding mesentery. This is 

 designated c^ in the figures. The other complete mesentery 

 becomes the mate of c\ It is referred to as c-. On the side of 

 the new directive plane toward a complete old bounding mesen- 

 tery the order of formation of the complete mesenteries is there- 

 fore as follows: c\ d, c^, c^. This order is apparent, through 

 differences in size of the mesenteries, in figures 9 and 10, repre- 

 senting sections at different levels of a single animal. The 

 order in which the new mesenteries become complete is some- 

 what different from the order of their appearance, the directives 

 usually being first to reach the esophagus, followed very shortly 

 by c^ C" very soon equals c^ in size, and these two become con- 

 nected with the esophagus at a somewhat later time. For a 

 long time their inner ends are free from the esophagus near the 

 aboral end of the latter. Occasionally the inner ends of c^ 

 and c* are united as described for the new directives. Instances 

 of the stage where all of the new complete mesenteries except c^ 

 and c^ are attached to the esophagus are represented in figs. 15, 

 18, and 31. As has been previously remarked by Carlgren 

 ('04, p. 52), it was probably this stage in regeneration which the 

 Hertwigs ('79, p. 82) took for a stage in ontogenetic development 

 in the case of two specimens of Adamsia. 



On the side of the first set of four toward an incomplete old 

 bounding mesentery, the next mesentery to appear is likewise 

 destined to become the outermost complete mesentery of the 

 new piece. The longitudinal muscle, when it appears, faces 

 toward the new directives, whereas the muscle of the outermost 

 mesentery adjacent to an old complete mesentery faces (see 

 above) toward the old part. This mesentery is c^. The next 

 to appear is the one designated c-. It is destined to pair with 

 c^; d, the mate of c^, appears very slightly after c-, or even simul- 

 taneously with it. An incomplete mesentery, {!), appears ad- 

 jacent to the incomplete bounding mesentery at a later period, 

 as described below. 



