202 DONALD WALTON DAVIS 



or character of the old mesenteries. Differences in size of the 

 members of a pair of mesenteries in the diagrams of this figure 

 indicate the order in which the mesenteries of the pair become 

 complete. Table 12 sets forth the frequency with which these 

 types occurred in regenerating pieces of different species. Gary's 

 regenerating specimens of Aiptasia and Cylista (?) belong to 

 type IV. The cases I have given of regeneration in S. luciae 

 which do not involve matching up of new with old complete 

 mesenteries are of Carlgren's types III, VI, or II. For con- 

 venience in indicating the order of appearance of these mesen- 

 teries, I have added to diagrams I and III the symbols by which 

 I have designated mesenteries occupying corresponding positions 

 with respect to the new directive plane. Using these symbols 

 for the different mesenteries, we may construct formulas for the 

 order of appearance as given by Carlgren in these different types, 

 thus: 



(I) c^, c^ d, c~, c* 

 (II) c\ d, c\ 

 (III) c\ d, c\ c\ c\ 



Carlgren's statements indicate that in (I) & and c^ appear nearly 

 simultaneously. In (III), c* appears only slightly after c\ and 

 & very soon after c-. It will be seen that the sequence of mesen- 

 teries in development given for type (III), as well as the order of 

 becoming complete, is the same that I have found to occur in 

 S. luciae except in cases where a complete old bounding mesentery 

 is present. 



Carlgren has proposed ('09, p. 41) an ingenious theory con- 

 cerning the relations of the types of arrangement of mesenteries 

 demonstrated in his regenerating specimens. For the arguments 

 he produces in its support, the reader is referred to Carlgren's 

 paper. I shall here simply outline the theory. 



Types I, VII, IX, and X show clearly bilateral arrangements 

 of the mesenteries in development. Type VIII is typically 

 biradial in form. Type I Carlgren takes to be the most primi- 

 tive. It parallels the Edwardsian method of ontogenetic de- 

 velopment except in that the presence of the old part inhibits 



