ASEXUAL REPRODUCTION IN SAGARTIA 187 



a new mesentery, c'', forming with the bounding mesentery a 

 non-directive pair. In the middle of the new area is a pair of 

 directive mesenteries, d, d. Between the directive and the new 

 bounding mesenteries, on either side, is a pair of non-directives, 

 c\ C-. Figure 16, representing a more aboral section, shows the 

 first cycle of incomplete mesenteries appearing in the primary 

 exocoels. Other cycles of incomplete mesenteries are formed 

 later. Where, under these conditions (as in specimen no. 26, 

 table 6), six mesenteries are regenerated, onl}^ one complete 

 non-directive is formed between the new directives and the old 

 bounding mesentery, and this one mates with the latter. I have 

 no specimen with the reduced number of complete mesenteries 

 on both sides of the new directives, but no doubt such instances 

 may be found. Only four new complete mesenteries would then 

 be developed. 



When division has occurred in two incomplete endocoels 

 leaving an incomplete mesentery adjacent to each boundary of 

 the old region, ten complete mesenteries are usually regenerated. 

 This is the case in the later regenerating zone of the specimen 

 (no. 81, table 7) shown in figures 15 and 16 (upper, right). In 

 the middle of the new area is a pair of directives, d, d. On 

 either side of this pair of directives are found two pairs of non- 

 directives, c^, c^ and c^ c^ Permanently incomplete new bound- 

 ing mesenteries, (/), (/) (fig. 16), are formed paring with the 

 old incomplete bounding mesenteries. These, new incomplete 

 mesenteries appear later than the complete mesenteries, and in 

 many specimens represented in the tables, they were lacking at 

 the time of killing. In later stages of regeneration they are 

 invariably found. They are frequently present in the aboral 

 region while lacking at levels nearer the oral disc. This is the 

 case in the specimen represented by figures 15 and 16. Other 

 incomplete mesenteries develop in pairs in the exocoels of the 

 new region. In three cases where both of the old bounding 

 mesenteries are incomplete (nos. 4a, 4b of table 3 and no. 79 

 of table 7) only eight complete non-directive mesenteries were 

 regenerated, and in one case (no. 76, table 7), but six. In 

 these specimens only one pair of complete non-directive meseii- 



