Anatomy of Gorgonid^. 153 



The gullet is shallow, with one to three extensive lateral 

 convolutions. It very closely resembles that of Briareum. In 

 both cases the shallowness of the gullet seems to be a neces- 

 sary consequence of the shallowness of the calicles. 



Muscular system. The retractor muscles are strong and 

 conspicuous. (See PI. X, fig. 6, g, g). They extend along 

 each mesentery from near the bases of the tentacles to near 

 the bottom of the calicles. The usual tentacular muscles are 

 present. 



Besides those muscles that have been described in previous 

 species, there appears to be a sort of sphincter muscle which 

 closes the invaginated bcdy wall over the retracted polyp- It 

 will be remembered that in retraction the" body wall is flexed 

 upon itself at the edge of the calicular opening so 

 as to form a sack above the gullet, in which the tentacles are 

 folded. The upper end or mouth of this sack would be 

 nearly as large as the calicular opening were it not for this 

 muscle which acts as a purse-string to close the mouth of the 

 sack. 



It is interesting to note the contrivances by which the soft 

 parts of the polyps are protected in the several species studied. 



In Briareum asbestinum the polyp sinks deep within the 

 calicle and the elasticity of the coenenchyma permits a partial 

 closing of the calicular opening, which leaves a small round 

 pore. 



In Plexaurella dichotoma the polyp does not sink so deeply 

 into the calicle, but the orifice is closed b}- the elasticity of the 

 ccenenchyma in such a way as to leave a slit-like aperture. 



In JSunicea muricata the calicular lips have an opercular 

 action, closing over the retracting polyp much as the lid of the 

 nest of the trap-door spider closes over the animal. 



In Eunicea tourncforti the polyp does not retract, but the 

 tentacles and oral surface are armed with spicules which make 

 them almost as hard as the general surface of the zoantho- 

 deme. 



In Rhifidigorgia jlabeUum and probably also in Muricea^ 



