32 A Guide to the Zoological Collections in the 



branchings : so that in this way the horny substance which 

 was originally on the outside of the base of the polyp 

 comes to occupy the central core of the polyp-colony. 

 Round about this horny axis of ectodermal origin masses of 

 calcareous spicules are deposited, and these often fuse to- 

 gether or interlace to form a thick rigid coral. Such a 

 coral, formed of both ectoderm and mesoderm, is found in 

 Gorgonia. 



The Alcyoniomorpha are divided into three Orders, 

 the Alcyonacea, the Pennatulacea, and the Gorgonacea. 



i. ANTHOZOA ALCYONIOMORPHA ALCYONACEA. 



[ara0£ 4]. 



In the Alcyonacea there is no horny central axis of 

 ectodermal origin, and the units of the polyp-colonies are 

 united either by a thick fleshy ccenosarc in the mesoderm 

 of which calcareous spicules are secreted, or by a hard 

 calcareous coenenchyma. The coenosarc is tunnelled by 

 canals which are continuations of the gastric cavities of 

 the polyps, and by these canals (" nutritive canals ") nu- 

 triment is distributed throughout the colony. The nu- 

 tritive canals are well seen in the vertical section of Alcyon 

 ium glaucum^ and in the transverse section of Spon- 

 godes, in Case 4. 



The Alcyonacea are represented in Case 4 by the fine 

 spirit specimen of Telesto arborea, by the series of dried 

 coralla (mesodermic) of Tubipora musica, by the spirit 

 specimens of Alcyonium^ Lobularia, and the fine series of 

 species of Spongodes, and by the dry specimens and draw- 

 ings of Heliopora. In Spongodes the colony has the form 

 of a bush, in which the coenosarc forms a root and stem 

 and branches, and the polyps occupy the sides and tips of 

 the branches like leaves or flowers. 



In Heliopora the coenenchyma has become calcified 

 and forms a crystalline stony mass, like the coral of a 

 Madreporarian. 



