228 DONALD WALTON DAVIS 



the side of a new directive plane which is toward an old incom- 

 plete bounding mesentery are usually produced two pairs of 

 complete non-directive mesenteries. On the side of the new 

 directive plane which is toward an old complete non-directive 

 bounding mesentery are commonly formed a pair of complete 

 non-directive mesenteries and a single complete mesentery which 

 forms a non-directive pair with the old bounding mesentery 

 (pp. 186, 188). The only common exception to the numbers of 

 complete mesenteries as stated consists in the omission of a pair 

 of complete mesenteries lateral to the new directives (pp. 187, 

 188, 191). The number of complete mesenteries formed in a 

 regenerating zone is thus strictly limited and almost invariable, 

 except through the influence of the old mesentery adjacent to 

 the boundary between old and new tissue. This mesentery, if 

 unpaired, exerts a perfectly definite determining influence upon 

 the course of regeneration, an influence which makes its appear- 

 ance soon after regeneration has begun and effects a normal 

 pairing of the mesenteries of the bounding region and usually a 

 regular arrangement of the pairs of different cycles in harmony 

 with those of other regions (p. 193). 



The order in which the new mesenteries appear and the order 

 in which they become attached to the esophagus (pp. 193 to 188, 

 201; see especially pp. 193, 196) do not correspond, and neither 

 agrees with the order of ontogenetic development described for 

 any Actinian whose transformation has been completely followed. 

 At a late period of regeneration a stage is passed through corre- 

 sponding with that described as a stage in the ontogeny of 

 Adamsia by Hertwig; but this is probably correctly interpreted 

 by Carlgren as a stage in regeneration (p. 194). 



In the course of regeneration incomplete mesenteries appear 

 in pairs in the normal positions (p. 194) . Where the old bounding 

 mesentery is an incomplete one a single new incomplete mesen- 

 tery of the same cycle is formed to pair with it. When division 

 has occurred in an incomplete endocoel of the second or lower 

 order close to a pair of complete mesenteries, no new incomplete 

 mesenteries of higher cycle are formed in the region limited by 

 the complete mesenteries and including the boundary between 



