ADVENTITIOUS REPRODUCTION IN HARENACTIS. 3 



portions of the mesenteries as protruded from the cut ends of 

 the pieces, or accomplished the same result by other means. 1 

 In the experiments of this summer greater care was taken to 

 make certain that all the muscles were removed, and the free 

 borders of the mesenteries in most cases the greater part of 

 the mesentery as well were cut away. After these operations 

 the pieces consisted of the body wall with only the bases of the 

 mesenteries, i. e., those portions which lie nearest the line of 

 attachment to the body wall. The nature of this operation is 

 indicated approximately in the diagrammatic Fig. 2. This repre- 

 sents a typical longitudinal section of the body wall of the 

 cylindrical piece: all the internal mesenterial structures between 

 the two broken lines are removed, leaving only narrow strips of 

 mesenterial tissue next to the body wall. 



Such pieces form rings in almost every case, and nearly all of 

 the rings give rise to tentacle groups. The result of the removal 

 of the mesenteries is the approximation and contact of the oral 

 and aboral cut ends of the body wall, as indicated in the optical 

 section, Fig. 3. Union occurs between these cut surfaces and 

 the body wall thus forms a closed ring with an opening through 

 the center and with no connection between the enteron and the 

 exterior. The enteric cavity becomes more or less distended 

 with water after closure, undoubtedly in consequence of the 

 passage of water through the body wall, and sooner or later a 

 peculiar rotation of the parts about a circular axis situated in 

 the enteric cavity of the ring occurs, as described in my earlier 

 paper ('096, pp. 356-357). The result of this rotation is a change 

 in the position of the line of union between the oral and aboral 

 ends from its original position around the central opening to the 

 outer surface of the ring (cf. Figs. 3 and 4 of the present paper; 

 in Fig. 4 the region of union between oral and aboral ends is 

 indicated by the very thin body wall which is formed of new 

 tissue). Very commonly the line of union, which is marked by 

 the formation of more or less new tissue, finally comes to occupy 

 a position somewhat upon the upper surface of the ring as this 



'oga, "Factors of Form Regulation in HarenaC'is attenuata, I., Wound 

 Reaction and Restitution in General and the Regional Factors in Oral Restitution," 

 Journ. Exp. Zoo/., VI., 4, 1909. 



, 'ogb, Figs. 2-5, Fig. 31, also pp. 373~37-4- 



