ASEXUAL REPRODUCTION IN SAGARTIA 205 



the esophagus. Previously the longitudinal muscles of the new- 

 mesenteries are not apparent, but about the time these mes- 

 enteries reach the esophagus the muscles rapidly develop and 

 the directives are distinguishable from the non-directives. The 

 order of events suggests that the development of mesenteries 

 into directives is determined by the presence of a siphono- 

 glyph. In a number of cases I have found a group of four small 

 mesenteries with the characteristic proportions of the first four 

 regularly formed in regeneration, but extending only a short 

 distance up and down the column. Elsewhere the column wall 

 and mesenteries gave no evidence of a division w^hich might have 

 given occasion for such a regenerating area. I interpret these 

 as regions of regeneration following comparatively slight injuries 

 to the body wall. In most of the instances the mesenteries are 

 small and have no indication of longitudinal muscles. In no 

 case do mesenteries in these sets show the characteristics of a 

 pair of directives. In one case apparently the two inner mesen- 

 teries of the four have the characteristics of non-directives. In 

 another instance two mesenteries only are formed. These are 

 long and slender and show no longitudinal muscle bands. They 

 reach the esophagus in a region where histological evidence of a 

 siphonoglyph is not present, although there was a slight groove 

 at that region of the mouth, as seen from the exterior and in 

 sections, and although a narrow white line, indicative of the 

 presence of a siphonoglyph, was to be seen in the living animal 

 extending part of the way from the groove toward the tentacular 

 zone of the disc. 



These observations suggest that the first four mesenteries 

 which form so constant a feature of the regeneration of S. 

 luciae arise independently of the siphonoglyph, and that con- 

 trary to Carlgren's 'hypothesis, no more mesenteries are formed 

 adjacent to the directive plane even in the absence of a siphono- 

 glyph. The order of events in S. luciae is as follows: fusion of 

 edges of the column, appearance of a set of four new mesenteries, 

 extension of these to the esophagus, formation of a siphonoglyph, 

 development of longitudinal muscles in positions which mark 

 out the inner members of the first set of four mesenteries as a 



