A8TER0IDE.E. 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 Gorgonidce, 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, massive, 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 

 m 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 ; ' 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 " synapticulae or 

 transverse props, extending across the loculi like the bars 

 of a grate." ^Nevertheless, there is no difficulty in recog- 

 nising the close resemblance that sucn 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. Pennatulidaz 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 



