30 A Guide to the Zoological Collections in the 



retracted, can be compared with the denuded and dried 

 coralla alongside. 



ill. ANTHOZOA ACTINIOMORPHA ANTIPATHARIA. 



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The Antipatharia constitute a small group of Ac- 

 tiniomorpha which, like the true corals, form branching 

 tree-like colonies supported by a rigid skeleton. The 

 skeleton of the Antipatharia differs from that of the Mad- 

 reporaria in being formed of horn instead of stone, and in 

 being developed only in the coenenchyma and not round 

 the polyps themselves, which are quite soft, like a sea- 

 anemone. The Antipatharian corallum, in short, much 

 resembles the corallum of the Gorgonacea next to be de- 

 scribed, the resemblance being so complete as to have 

 misled the older zoologists into classing the Antipatharia 

 with the Alcyonaria. When, however, the living polyps 

 are examined, the Antipatharia are found to agree with 

 the Actiniaria in having tentacles in sixes or multiples of 

 six, and in having usually numerous septa, instead of, like 

 the Alcyonaria^ eight tentacles and eight septa. 



The black skeleton or corallum of the Antipatharia^ 

 moreover, can be at once distinguished from that of the 

 Gorgonacea in being densely covered with little thorns. 



The Antipatharia are represented in Case 7 by the 

 dried tree-like skeletons of Antipathes and Cirrhipathes, 

 by the fine spirit-specimens of the same genera, in which 

 the little polyps with their coenenchyma can be seen in- 

 vesting all the twigs and branches of the corallum like a 

 soft bark, and by the fine specimens of Bathypathes, a 

 deep-sea genus. 



Bathypathes is a remarkable type which is distinguished 

 from all other Actiniomorpha by exhibiting the phenome- 

 non, already described, of dimorphism : that is to say, 

 in every colony some of the units are specially modified to 

 perform only reproductive functions (reproductive zooids 



