ASTBROIDEiE. 487 



some it constitutes a free axis, virgate or primately divided 

 and varying in thickness ; in others it is attached, simple 

 or branched, and plant-like, as in Gorgoiiidce, from which 

 circumstance the name of " Sea-shrubs " has been applied 

 to them. In the Gorgonia we have, in addition to the 

 basal corallum, a deposition of tissue secretions, sclero- 

 dermic spicules appear within the substance of the in- 

 vesting membrane, and when the animal is dried, and the 

 soft parts washed away, a thin layer of calcareous spicules 

 is seen adhering to the horny sclerobasis. M. Valen- 

 ciennes made out five kinds of spicules, or sclerites, which 

 he severally designates capitate, fusiform, mass^'ve, stellate, 

 and squamous. These spicules form interesting objects 

 for the microscope, mounted dry or in balsam. " The 

 parts of a typical coralite are these : first, an outer wall, or 

 ' theca,' somewhat cylindrical in form, terminating distally 

 in a cup-like excavation, or ' calice,' and having its central 

 axis traversed by a columella. The space between this 

 and the theca is divided into loculi, or chambers, by a 

 number of radiating vertical partitions, the septa. These 

 do not, in certain instances, quite reach the columella, but 

 ■ are broken up into upright pillars or pali, arranged in one, 

 two, or more circular rows termed ' coronets j ' all of 

 which are best brought into view by transverse section." 

 Longitudinal division of a corallite shows certain modifi- 

 cations and changes in the partitions, or dissepiments ; and 

 the septa are seen to be covered with " styliform or echi- 

 nulate processes," which meet to form " synapticulse or 

 transverse props, extending across the loculi like the bars 

 of a grate.'' J^evertheless, there is no difficulty in recog- 

 nising the close resemblance that such an organism pre- 

 sents to the typical Actinia, and they have accordingly 

 been classed with the Actinozoa. 



The Gorgonida, are permanently fixed, as are many other 

 corallitic actinozoa, and multiply by continuous gemma- 

 tion. As to their muscular system, most of them appear 

 to be well endowed in this particular. Pennatulidce pos- 

 sess so much muscular contractibility, that Mr. Darwin 

 relates, that on the south coast of America he observed 

 '* a Sea-pen which, on being touched, forcibly drew back 

 into the sand some inches of its compound, polypi-covered 



