Wound Reparation—A ctinian Tentacles 209 
tracted condition of such fragments and in absence of internal 
pressure, there was usually little suggestion of the nipple form at 
the distal tip. 
This same experiment was performed upon tentacles of Aiptasia. 
The following case 1s a typical one. A large tentacle was excised 
near its base and ligated onto the hydrostatic tube. A sharp con- 
traction took place, the tentacle being reduced to about one-fourth 
its original extended dimensions, both as to length and diameter. 
After fifteen minutes, during which the tentacle remained in this 
contracted condition, internal pressure was applied. Under the 
influence of 30 mm. water pressure the contraction was partially 
overcome and the tentacle swelled to about twice the length and 
diameter which it possessed just before the application of the pres- 
sure, that is, to about one-half its dimensions before excision. 
This expansion appeared to be perfectly passive on the part of the 
tentacle—rather a direct mechanical effect of the internal pressure 
than a result of any spontaneous extension of the tissues them- 
selves. While in this stretched condition, about two-thirds of the 
distal end of the tentacle was quickly clipped off. Instantly—in 
the fraction of a second, and before the water in the glass tube 
could fall more than some § mm.—the cut distal end of the stump 
of tentacle closed and a prominent nipple was formed. ‘The 
tentacle as it appeared at this moment is shown in Fig. 11 (Plate 
2). Having remained in this condition for several seconds, the 
tentacle then shortened abruptly, the nipple disappeared, and 
the distal end became broadly open, allowing the water col- 
umn to fall to zero. At frequent intervals thereafter tendency 
to extend was noted and at such moments water was introduced 
into the tube. Sometimes no marked extension followed and the 
water merely ran through the tentacle and escaped at the open 
cut end. But, four times within ten minutes, extension accom- 
panied by closing of the cut end and formation of the nipple did 
take place and the conditions of Fig. 11 were repeated. Each 
time the nipple sustained a pressure of some 30 mm. of water with 
only slight leakage, or none at all. 
To demonstrate the closing of the cut distal end and the for- 
mation of the nipple in excised tentacles of Aiptasia the use of the 
