210 Herbert W. Rand 
hydrostatic apparatus was essential. When a piece of tentacle, 
cut at both ends, was allowed merely to lie upon the bottom of the 
aquarium, it remained in a strongly contracted condition for 
hours—so contracted that water could not be injected at the prox- 
imal end by means of a pipette as was done for Condylactis. From 
the instant of cutting the distal end was virtually closed owing 
to this condition of general contraction. 
The behavior of pieces of Condylactis tentacles and pieces of 
Aiptasia tentacles under the influence of artificial internal pressure 
is substantially the same. Such differences as appeared are 
parallel with differences noted in the behavior of tentacle stumps 
left attached to the columns in the two species. Whether attached 
naturally to the column or artificially to the hydrostatic tube, 
the distal cut end of an Aiptasia tentacle closes and forms the 
nipple much more promptly and decisively than does the Condy- 
lactis tentacle under similar circumstances. Further, the nipple 
is a slightly more conspicuous and constant feature in Aiptasia 
than in Condylactis. 
A fairly definite difference was observed in the behavior of those 
pieces of Condylactis tentacles which were attached to the hydro- 
static tube and those which were allowed to lie upon the bottom 
of the aquarium. Under the latter condition contraction in length 
was the conspicuous feature and when the contracted tentacle 
relaxed somewhat there was commonly only a moderate increase 
in length, while the diameter remained large (Figs. 13-15). In the 
case of a piece ligated onto the tube, contraction in diameter was 
more marked and when the piece extended it was usually an exten- 
sion chiefly in length, the diameter remaining much contracted 
except as it was increased mechanically by internal water pres- 
sure (Fig. g). 
DISCUSSION AND SUMMARY 
What is the means by which this prompt and characteristic 
closing of a distal cut end of a tentacle is effected? There can 
be hardly any doubt that the initial closing, which is usually accom- 
panied by the formation of a nipple, is chiefly dependent upon 
contraction of muscle fibers. ‘The following facts point toward 
