210 



ACTINOZOA. 



suppose that the latter completely invests the soft 

 parts of the animal, the corallum of Tubipora 

 being a true tissue secretion. Its horizontal outer 

 plates are suggestive of a distinct analogy to the 

 Tabulata, nor are traces of internal tabulae wholly 

 wanting. The characteristic form of Tubipora 

 seems due to the periodic budding of zooids from 

 the distal surface of the plates, while at the same 

 time certain of the older corallites continue to 

 increase in height. But neither the minute struc- 

 ture nor development of this interesting genus have 

 yet received proper attentioD. 



The Gorgonidce differ from all other Alcyonaria 



in having an erect branching coenosarc, firmly 



rooted by its expanded proximal extremity {fig. 



37, c). Those which possess a horny sclerobasis 



have been by many writers confounded with the 



Anhpathidce; but, apart from the anatomical 



features of their polypes, they may at once be 



known from the latter by the more or less sulcate 



aspect presented by the surface of the sclerobasis. 



the modifications which this structure displays in 



Coralhum,lsis,Mopsea,tm& Melitcea have already 



received a brief notice. It may suffice to add that 



very exaggerated conceptions seem to prevail as to 



the height which the horny Gorgonidce are capable 



ot attaining. It is doubtful whether their largest 



trees ever rise to more than five or six feet, 



yet some have been reputed to rival oaks in 



size, an assumption which, however incredible, is, 



nevertheless, not inconsistent with theoretical con- 

 siderations. 



The Alcyonaria, as a group, seem destitute of 

 locomotive power, though one family of this order, 

 the Fennatulido3, have been often regarded as 



