Form Regulation in Harenactis attenuata 365 
nearest the line of union and so nearest the original aboral end 
often develop less rapidly than the others. 
VI Figs. 21 to 23. The piece was from the middle region of 
the body and repeated extrusion and removal of mesenterial 
organs preceded closure, only a small part of the organs remaining. 
Fig. 21 shows a stage eleven days after section: the line of union 
is at the equator and the tentacle groups are on the original oral 
23 
Fics. 21-23 
end of the body-wall. Fig. 22 is a stage eight days later. ‘This 
piece produced longer tentacles than any other observed; the 
two longest tentacles in group } (Fig. 22) were Io to 12 mm. 
in length. Fig. 23 shows the relation of group b to the line 
of union, the lower side in the figure being the oral, the upper 
side the aboral. The other groups show similar relations and it 
should be noted also that in all three groups the tentacle which 
