ADVENTITIOUS REPRODUCTION IN HARENACTIS. 5 



of union of the original distal and proximal ends of the piece, 

 but failing to attain the usual form because of the peculiar con- 

 ditions under which they arose. 



In returning to these experiments this summer, I hoped to 

 obtain tentacle groups which should approach more closely the 

 usual form of Harenactis and thus leave no doubt that these 

 outgrowths really represent new polarities, in short, that these 

 phenomena in rings are really a form of asexual reproduction related 

 to certain cases of the formation of adventitious structures in 

 plants. These hopes were fully realized in one case, to be de- 

 scribed below, and other tentacle groups among the large number 

 obtained showed various points of interest. 



DESCRIPTION OF EXPERIMENTS. 



The case of greatest interest is one in \vhich only one group of 

 tentacles appeared upon the whole ring. This group was situated 

 wholly upon one side probably the oral of the line of union, 

 was radially symmetrical from the beginning and at first pos- 

 sessed seven or eight tentacles. During its growth, how r ever, 

 new tentacles appeared until the number reached sixteen. The 

 tentacles were regularly arranged about a disc similar in appear- 

 ance to that of the normal animal and in the center of the disc 

 a mouth, opening into a short esophagus, appeared. On the 

 disc sixteen mesenteries could be counted, most or perhaps all 

 of these being new, as was evident both from their appearance 

 and relation to other parts and from the impossibility that sixteen 

 of the twenty-four old mesenteries should be involved in this 

 new development from a small area localized on one side of the 

 ring. Fig. 5 shows this new disc with the sixteen tentacles as it 

 appeared twenty days after the operation. The line of union 

 between the original oral and aboral ends of the piece is indicated 

 by the dotted line. This new individual differs from the full 

 grown animal in nature in the smaller number and unequal length 

 of the tentacles and in the absence of a proximal end, but there 

 can be no doubt that it represents a new body-axis, a new polarity. 



After the formation of the disc it gradually became elevated 

 above the surface of the ring by the growth of a cylindrical 

 column beneath it. Fig. 6 is a diagrammatic optical section 



