210 ACTINOZOA. 



suppose that the latter completely invests the soft 

 parts of the animal, the corallum of Tabipora 

 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 attention. 



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 

 AntipatMdce ; 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 w^hich this structure displays in 

 Corallium,lsis,Mopsea,Sind Melitcea have already 

 received a brief notice. It may suffice to add that 

 very exaggerated concei^tions seem to prevail as to 

 the height which the horny Gorgonidce are capable 

 of 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 Alcyonaiia, as a group, seem destitute of 

 locomotive power, though one family of this order, 

 the Pennatulidce, have been often regarded as 



I 



