22 



sequently a considerable space must be allowed between their 

 point of origin from the Scyphomedusse and the immediate 

 common ancestor of the Zoantharia and Alcyonaria. This 

 form, which must have been polype-like in appearance (the 

 medusiform condition having been finally lost some way 

 back), was intermediate in its characters between a Sea- 

 Anemone and a simple Alcyonarian, but less difi'erentiated 

 than either. It must have possessed the typical Actinozoon 

 arrangement of internal cavities — a stomodseum or gastric 

 tube, and an enteron sub-divided by radiating mesenteries- — 

 as this structure is found in both the Zoantharia and the 

 Alcyonaria. It probably had the power of budding off 

 polypes like itself, which were not free-swimming, but 

 remained fixed to the parent form. From this *' Proto- 

 polype " two ancestral series must have arisen, the one lead- 

 ing onward to the Proto-Alcyonaria, and through them to 

 the various groups of Alcyonarians now known, and the 

 other diverging to become the ancestors of the Antipatharia, 

 the Actiniaria, and the Madreporaria. 



The Proto-Alcyonaria must have acquired the character of 

 having only eight tentacles and the same number of mesen- 

 teries, while the tentacles became more or less pinnate or 

 fringed. This ancestral stock is most nearly represented at 

 the present day by such simple Alcyonaria as the genera 

 Monoxeniciy Haimeaf and Hartea; while the remaining 

 Alcyonarians have advanced from this point along two diver- 

 gent series — the one branch (to the right in the table) 

 leading through such forms as Sarcodictyon and Clavularia 

 to the Tubiporidae, and the second forming the common stem 

 from which the ancestral Helioporidae, Alcyonidae, Gorgon- 

 idse, and Pennatulidae, have arisen. In the first of these 

 series the property was acquired of forming calcareous 

 deposits in the mesoderm (or deeper layer of the ectoderm) 

 of the body wall. They are found in the form of detached but 



