186 DONALD WALTON DAVIS 
that, had the natural division occurred in some other plane, 
adequate evidence of the position of the plane of fission would 
not have persisted to the time of killing. Still others are re- 
generating individuals resulting from artificial cuts. The last 
mentioned are pointed out in the explanations of tables 7 and 8. 
It will be seen that they regenerate in the same general manner 
as if they had divided naturally in a corresponding plane, but ap- 
parently show wider variations in the number of new mesenteries. 
Table 9 shows the frequency of different numbers of new com- 
plete mesenteries, based upon the specimens represented in 
tables 3 to 7. I include here as complete mesenteries not only 
those actually reaching the esophagus, but also mesenteries now 
incomplete but destined to become complete. These are, in 
nearly all cases, readily distinguishable from true incomplete 
mesenteries whatever the stage of regeneration. For incomplete 
mesenteries appear only after those destined to become complete 
have reached relatively large size, and they develop more slowly 
than the complete ones. Furthermore, the members of a pair of 
new incomplete mesenteries appear simultaneously and remain 
of equal size during their growth; while members of a pair of 
complete mesenteries reach such a state of equality only late in 
regeneration. Since all of the complete mesenteries destined to 
be formed in a regenerating region appear quite promptly, their 
number may be safely judged almost from the beginning. These 
features are illustrated in figures 23 to 30. The numbers of new 
mesenteries actually complete is indicated in the tables of 
mesenteric formulas in connection with each regenerating zone. 
Where complete old non-directive mesenteries occupied both 
boundaries, regeneration involved the production of eight com- 
plete mesenteries in twenty-five cases and six complete mesen- 
teries in two cases (table 9). The character and arrangement of 
the eight mesenteries commonly formed may be made clear with 
the aid of figure 15, representing specimen no. 64 of table 7. The 
older of the two regenerating sectors, occupying about two-fifths 
of the area of the cross-section (lower left), is limited by two old 
complete bounding mesenteries c, c. On either side of this 
regenerating region, adjacent to the old bounding mesentery, is 
