Anatomy of Gorgonid^e. 105 



Each tentacular muscle bundle is broken up into fibres 

 which are distributed over a great part of the surface of the 

 tentacles and reach even to the tentacular papillae, although, 

 as has been said, these latter do not seem to retract during 

 Hfe. 



It is by no means easy to state clearly the mechanism of 

 retraction and the relation of the various parts during and 

 after the. process. By analyzing the different stages of retrac- 

 tion, we may be able to understand these points. 



The tentacles are first shortened and at the same time 

 reduced in diameter. The shortening is effected by the main 

 tentacular muscles, while the lateral fibres constrict the tenta- 

 cle and force out the water. By this means the bulk and 

 lengfth of each tentacle is much reduced. 



Next, the retractor muscles pulling from the bottom of the 

 calicle cause the gullet and polyp wall to sink into the calicle. 

 The gullec is thrown into numerous convulutions and the body 

 wall is flexed upon itself at the edge of the calicle. The 

 tentacles curl upon themselves and now occupy a sort of sack 

 formed by the invaginated body wall which by its elasticity 

 binds them together into a firm bundle. At the bottom of 

 this sack, is the mouth. The retracted pol3'p is shown in fig. 

 6, PI. I. 



Sphincter muscle. This is a number of muscle bands which 

 are found on the oral surface of the polyp, and in combination 

 form an octagonal figure around its mouth. Their function is 

 to close the latter. 



Gullet muscles are horizontal muscle bands found surround- 

 ing the outer portion of the gullet wall. They are found 

 beneath the endodermal investmeni of the gullet. They do 

 not seem to be merely a portion of the retractor muscles 

 which pass into the gullet walls', but a separate set altogether. 



I. This is the idea presented bj Pouchet and Mey^vre. Speaking of the 

 retractor muscles whicli thev call "muscles longitudinaux," thev say : "Un 

 certain nombre de fibres s'ecartent un peu, viennent s'(5taler en ^ventail sur la 

 face externe de la paroi de I'estomac, dans sa portion sup;?rieure." Contribu- 

 tion a I'Anatomie des Alcjonaires. Pp. 302, 303. 



