Form Regulation in Harenactis attenuata 359 
their bases, which correspond in direction of growth to aboral 
tentacles (a, Fig. 8, also the left half of Fig. 9), and finally one 
tentacle, which is apparently oral-aboral, has appeared (4, Fig. 
8): it arises at the line of union and is evidently formed by the 
fusion of two tentacles one of which was oral, the other aboral. 
In the later history of this piece the aboral tentacles increased 
somewhat in length, but within a week after the stage of Fig. 8 
a0 3b 
decrease in the distension became marked and all tentacles began 
to atrophy at the tips, and gradual collapse and finally death fol- 
lowed. 
The following are the chief points of interest in this case: ten- 
tacles do not appear about the whole circumference, but are 
grouped; aboral tentacles appear later than oral—except in the 
single oral-aboral tentacle, where the two parts evidently arose 
at the same time—and are in all cases opposite oral tentacles, 
though the aboral are less numerous than the oral tentacles. 
