Form Regulation in Harenactis attenuata 367 
and an isolated tentacle at d are present; eight days later (Fig. 25) 
the tentacle at d and all but one of the tentacles in the group c 
have disappeared. Figs. 26 and 27 show the relations of groups a 
and } (Fig. 25) to the line of union. In all the groups the ten- 
tacle or tentacles (group a) lying nearest the line of union appear 
later than the others in the earlier stages. In group a two ten- 
tacles are shorter than the others in the earlier stages (Fig. 24) 
but later one of these attains the same length as the others (Fig. 
26). 
After twenty-four days this piece was almost completely col- 
lapsed and death followed a few days later. 
VUI Fig. 28. This piece was also taken from the middle 
region of the body and a large part of the mesenterial organs was 
removed before closure. In Fig. 28 nineteen days after section, 
the line of union is just above the equator and a single group of 
tentacles appears just below, 1. e., on the oral side of it. In this 
case the four tentacles of the group all appeared at the same time 
and are all equal in length. No other tentacles appeared and the 
piece soon began to collapse and degenerate. 
IX Figs. 29 and 30. This case is the most remarkable of all 
observed and is the only one of its kind which [succeeded in obtain- 
ing. It was taken from the middle of the body and most of the 
mesenterial organs were removed before closure. Fig. 29 shows 
its condition fifteen days after section. The line of union lies 
above the equator in the figure and just below (oral to) it are six 
complete circles of tentacles: three of these, a, 6 and c are alike 
and consist of six tentacles each; group d possesses only five ten- 
tacles, group e eight and group / four. In all the groups the ten- 
tacles are arranged symmetrically with respect to a line through 
the group parallel to the line of union. Fig. 30 shows the arrange- 
ment in groups a, b and c and the relation to the line of union. The 
tentacles all appeared at the same time and are all equal in 
length. 
But the most interesting feature of this case is the presence in 
the five groups a-e of a conical outgrowth in the middle of the 
disc. ‘This structure is shorter and more blunt than the tentacles 
and does not react to contact like the tentacles: its appearance in 
