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Their tentacles are lobed all around the margin, and are much more complicated in structure than those of the preceding Polyps. According to the relative complication of their structure, these animals are classified in the following order: Halcyonoids: eight tentacles in pairs, lobed around the margin; always combined in large communities, some of which are free and movable like single animals.
Another remarkable feature among the Madrepores consists in the prominence of one of the Polyps on the summit of the branches, showing a kind of subordination of the whole community to these larger individuals, and thus sustaining the view expressed above, that the combination of many individuals into a connected community is among Polyps a character of superiority when contrasted with the isolation of the Actiniae;. In the Sea-Fans, the Halcyonoids, as they are called in our classification, the number of tentacles is always eight, four of which are already present at the time of their birth, arranged in pairs, while the other four are added later.
In the Class of Polyps there are but two Orders, the Actinoids and the Halcyonoids; and I have already said so much of the structure of Polyps that I think I need not repeat my remarks here in order to show the relation between these groups.
Here the comparison is easily made; it is simply the complication and number of identical parts that make the difference between the Orders. The Actinoids stand lowest from the simple character and indefinite increase of these parts; while the Halcyonoids, with their eight lobed tentacles, corresponding to the same number of internal divisions, are placed above them.
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