60 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



ments toward the ambulacral groove, and then again straighten out as quick as light- 

 ning. Some of the groups opposite each other usually whip inward toward the fur- 

 row at the same time, but no flexing inward of the pinnules proceeding along the arms 

 can be observed. Small particles are fastened to the tentacles by the secretion of 

 unicellular mucous glands opening on the papillae, and with rapid motions of the 

 tentacles are cast into the ambulacral groove where the ciliary current catches them 

 and carries them to the mouth. 



Sensory hairs are also found on the tentacles, and it has been supposed that these 

 serve as sensory organs. The function of the tentacles, according to Gislen, is prob- 

 ably in reality manifold. First, they are certainly of considerable importance hi 

 respiration. Second, the mucus secretion, as pointed out above, serves to fasten 

 the falling grains of plankton or detritus upon the tentacles temporarily. Third, 

 the sensory cilia serve presumably in some way as an organ for taste and feeling. 

 When Gislen dropped picric acid upon them the arms were flexed and relaxed violent- 

 ly ; when he added a few drops of sublimate the arms were also rapidly bent and twisted, 

 the pinnules were stretched out, and the animal made swimming motions as if hi an 

 endeavor to escape. On a third occasion quinine sulphate with'a^few grains of car- 

 mine was added. The arms were waved actively to and fro, the pinnules were flexed 

 in to the sides of the arms or rubbed against each other, or laid over the place where 

 the drops had fallen, the arms were turned upside down, with the evident intention 

 of getting rid of the unpleasant matter. When old putrefying crab liver was added 

 to the fluid containing the grains of carmine the pinnules were flexed hi toward the 

 sides of the arms. This seemed to Gislen to indicate that a sense of taste is present 

 which presumably may be considered as localized hi the sensory hairs of the papillae 

 of the tentacles. 



Gislen was unable to determine definitely whether, as maintained by Reichen- 

 sperger, the secretion of the papillae of the tentacles is poisonous. He allowed 

 living pinnules to lie in contact with freshly caught plankton (Ephyrae, peridineans, 

 diatoms, and Plutei) but was unable to ascertain that any rapid unconsciousness or 

 toxic action took place. A small Cladonema seemed to make motions of escaping 

 when touched by a tentacle, but usually the tentacle bent away from the irritating 

 object. 



In the intestine of Heliometra glacialis Gislen has found quantities of copepods. 

 The copepods have a tolerably strong power of motion of their own, and he said it is 

 very probable that hi this case the secretion of the papillae of the tentacles hi some 

 way paralyzes the prey as otherwise it is difficult to imagine how the relatively weak 

 ciliary currents can transport the captured prey to the mouth. 



The most proximal of the tentacles in each of the groups of three is the shortest 

 and is directed straight upward, the middle one is longer and extends obliquely out- 

 ward, and the most distal is the longest and is directed straight outward. On the 

 arms this differentiation is indistinct, or is not marked at all. In the proximal parts 

 of the arms and on the disk the tentacles are unbranched. The tentacles are oftei> 

 more or less contracted, but at the maximum extension the longest tentacle reaches 

 from 0.5 to 0.7 mm. As the pinnules are placed at a distance of from 1.0 to 1.4 mm. 

 from each other, with the maximum extension of the tentacles the region between the 

 pinnules can be swept completely clean 



