336 J. M. D. OLMSTED 



thus pulling the body forwards, and immediately another tentacle 

 is attached above the first. There is no twisting of the tentacles 

 such as Clark ('99) describes for Synapta inhaerens and S. 

 roseola. The adhesion to the glass is so strong that a tentacle 

 presents the appearance of being almost torn away when it 

 finally lets go. The effectiveness of the pull of any tentacle 

 ceases when another tentacle, attached higher than the first, be- 

 gins in its turn to contract and pull the body up, yet an attached 

 tentacle seldom loosens its hold until it has assumed an V shape, 

 the proximal end having reached the same level as the distal 

 end. This is what one would expect if the tentacles were at- 

 tached to the glass merely by some adhesive substance and not 

 by muscular action. If there were actual suction, such as that 

 by which a mollusk clings to the substrate, circular, or possibly 

 radial, muscles would be required to lift a portion of the tentacle 

 away from the surface to create suction, and in that case release 

 would probably occur as soon as the pull on the tentacle ceased. 

 This is exactly the point which, I think, makes Semon's ('87, p. 

 283) explanation wrong. He thinks that "die Anheftung ge- 

 schieht, indem hierdurch beim Nachlassen des Druckes an ver- 

 schiedenen Stellen zwischen Glaswand mid der unebenen elasti- 

 schen Haut der Tentakel leere Raume oder weningstens Raume 

 entstehen, in denen das Wasser sich unter geringerem Druck be- 

 findet als das umgebende Medium." Since the tentacles remain 

 attached after they cease to be effective in pulling the animal 

 forward, and have to be fairly torn away from their attachment, 

 it seems probable that muscular action plays no part in the ad- 

 hesion of a tentacle to a surface. This is in accord with the re- 

 sults of anatomical investigations, namely that longitudinal 

 muscles are in all probability the only muscles present in the 

 tentacles (Clark, '07, p. 45). Synaptulas will hang so firmly 

 attached to the wall of a dish that they can be shaken' and the 

 water quite severely agitated before they will loosen their hold. 

 A Synaptula 4 cm. long can crawl up a vertical glass wall carry- 

 ing in sea-water a piece of iron weighing 30 mgm. in air (ca. 

 26 mgm. in sea-water) tied to its posterior end. 



