232 C. W. Hahn. 



mortality was high, because of unfavorable conditions in the 

 aquarium in which they were placed, and only three polyps 

 survived. Further, two of these were insufficiently regenerated 

 to show the character of the new mesenteries, but the third was 

 clearly a diglyphic polyp with one pair of directives in the old 

 tissue and one in the new, as expected. 



The fragments cut so as to exclude directives did somewhat 

 better. Ten polyps were reared from them. Eight of the ten 

 were clearly monoglyphic, with the directives always in the new 

 tissue; a ninth polyp was insufficiently regenerated, but it had 

 a pair of mesenteries on the regenerated side, which gave some 

 indications of being directives. If so, this polyp is similar in 

 character to the eight previously mentioned; if not, it is aglyphic. 

 The tenth polyp was diglyphic, but quite asymmetrical in char- 

 acter, one of the two pairs of directive mesenteries arising close 

 to the boundary between the old and the new tissue. It is impos- 

 sible to say whether a pair of directives was accidentally included 

 in the fragment from which this polyp developed or whether 

 there arose simultaneously two areas of regeneration, each of 

 which produced a pair of directive mesenteries. 



This direct experiment, incomplete though it is, supports the 

 hypothesis based on the experiments previously described. It 

 indicates that the dimorphism found in Metridia asexually pro- 

 duced is not dependent upon the monoglyphic or diglyphic char- 

 acter of the parent polyp, but upon whether the parent fragment 

 does or does not contain a portion of a siphonoglyph system. It 

 harmonizes, likewise, with the observations of Carlgren ('04) on 

 regeneration in Sagartia and other actinians and supports the 

 idea advanced earlier by Carlgren ('93) and supported by Parker 

 ('97), that the dimorphism of actinians is an incident of asexual 

 reproduction. 



As a control of the experiments examination was made of nine 

 spontaneously regenerated polyps collected at Lynn, Mass. 

 This yielded results closely similar to those obtained from the 

 artificially regenerated polyps. One of the polyps was inde- 

 terminable; one was diglyphic, with one pair of directives in the 

 old and one in the new tissue; and seven were monoglyphic. . Of 

 the seven monoglyphic polyps, five had the directives attached 

 to what was unmistakably the regenerated portion of the body- 

 wall, while in the remaining two old and new tissue could not be 



