ASEXUAL REPRODUCTION IN SAGARTIA 193 



artificially cut. Of the latter I have used only such as show 

 clearly the distinction between new and old sectors and are not 

 complicated by the presence of mesenteries extending through 

 only part of the length of the column. 



About three days after fission has become complete, two 

 mesenteries appear approximately in the middle of the space 

 between the two old bounding mesenteries. This space may 

 appear much like an ordinary endocoel (fig. 4), but is usually 

 somewhat wider. At this stage the two new mesenteries are 

 sometimes (as in the specimen referred to) united by their inner 

 edges forming a loop. Occasionally they retain this connection 

 until they are complete orally and have well-developed longi- 

 tudinal muscles; but usually they soon separate at the tips, as 

 indicated in figure 5, which represents a more aboral section 

 of the animal shown in figure 4, Very soon after this two other 

 mesenteries appear between the first two. This establishes a set 

 of four mesenteries, which retain the same relative size nearly 

 up to the time when they become complete. This set of four is 

 a striking feature of the regenerating zone for a considerable 

 period even after other mesenteries have appeared. It probably 

 corresponds with the group of four mesenteries found in S. 

 davisi by Torrey and Mery ('04) and represented in figure 5 of 

 their paper. These four mesenteries appear in their character- 

 istic relations in the photographs shown in my figures 7 and 8. 



The inner members of this set of four ordinarily become com- 

 plete slightly in advance of the outermost ones. They form the 

 directive mesenteries. The outer members of the set of four be- 

 come complete and remain the nearest complete non-directives 

 on either side of the new directive pair. They are the mesenteries 

 referred to as c^ in the account of the mesenteries of the new region, 

 and are so labeled in the figures. The first four mesenteries of the 

 new region are formed in the order described, no matter in what 

 spaces division has occurred. The order of development of 

 additional complete mesenteries, as well as their number, de- 

 pends chiefly upon the old bounding mesenteries. 



As shown above (p. 186), on the side of a regenerating region 

 adjacent to a complete old bounding mesentery, two additional 



