ALCYONOID POLYPS. 



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In a few species, the axis is partly or wholly calcareous. In 

 the Isis family, it is made up of a series of nodes and inter- 

 nodes. The former, in the genus Isis, are white, calcareous, 

 furrowed or fluted pieces ; and the latter are smaller and horn- 



ISIS HiriT 



like in nature, as illustrated in the preceding figures. In the 

 branching stem here figured, the main stem and the branch 

 on the left are smiply the axis, bare of the polyp-layer or cor- 

 tex ; while the branch on the right, with the surface dotted, 

 has the cortex complete, and the dots are the sites of the con- 

 tracted polyps. The circular figure below is a transverse sec- 



F 



